Siblings Share the Throne

"Hullo! Although they're King and Queen, they're brother and sister, not married to one another!"

— Shasta on King Edmund and Queen Susan, The Horse and His Boy

Typically in fiction, royal families abide by the tradition of primogeniture — the first-born son, barring a sudden, untimely death, gets to inherit the throne. In more progressive societies, a first-born daughter can get it, but her younger siblings are still out of luck. It's where the whole concept of "the heir and the spare" comes from — you need many spares in case that sudden, untimely death happens, but only one child can be the heir.

Then you have these cases — instead of an heir and a spare, you just have multiple heirs. Siblings grow up sharing everything, after all — why not let them share a kingdom?

This can also help to diffuse potential Succession Crises. Under normal succession, a younger sibling would inherit only after their elder's children and grandchildren. This can, and often does, lead to hostility and disputes from younger brothers or sisters who know that they will never hold power as long as their sibling's progeny is in the way — the Evil Uncle who schemes against his royal brother's sons is a narrative mainstay for this reason. Arrangements of this sort, with power distributed amongst different siblings, help to avoid such unpleasantness, although they can produce their own complications when deciding how to distribute power in the next generation among all of the rulers' own children.

Just like how a Board has a Chairman, ruling siblings can have one (almost always the eldest, of course) who slightly outranks the others and can resolve disputes, but they still share responsibility for the kingdom, hold equal titles of Kings and/or Queens, get to make decisions together, and none are considered subjects of any of the others or have to bow to the others.

You'll often find this set-up in the Backstory (where it most likely ended in disaster, creating the conflict the story needs to fix) or as an Ending Trope so that the writers can allow a Brother–Sister Team to share the Standard Hero Reward equally at the end (where it will presumably end in success).

The historians refer to this type of arrangement as "coregency."

Compare Ruling Couple, wherein the King and Queen are married but wield equal power.

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Examples:

Arts

• Medici Chapels: Lorenzo and Giuliano were this in real life, which their portraits reflect. The "New Sacristy", where their tombs are located, lavishes them with an equal measure of detail, befitting their status. Both brothers wear regal capes and have their tombs ornamented by paired, matching, allegorical sculptures.

Comic Books

• Castelmaure: Of the four surviving children of the king, the conjoined twins are the ones who eventually rule over the kingdom.
• Wonder Woman: Diana's mother, Hippolyta, originally co-ruled the Amazons with her sister Antiope. The latter eventually left with her own band of followers, who became the Bana-Mighdall.

Fan Works

• Codex Equus:
  • The sisters Blue Diadem, Yellow Barding, White Corona, and Rose Regalia co-founded the Coronan Imperium in their mother's name, and ruled it together as the Radiant Tetrarchy.
  • Blanche Amour and Cramoisie , fraternal twin sisters, are the founders, and co-rulers of the Necrocracy of Royaumort. Blanche Amour rules over the Death cults, while Cramoisie rules over the vampires of the Court of Blood.
• JoJo New Universe: While Zanac is in place to be the sole king of Re-Estize, in practice he intends to share the actual ruling of the kingdom with his two sisters.
• Queens of Mewni Spinoffs: Post-retcon, Heliador's sister Eureka survived infancy but was a very sick child. Seeing this and also not wanting either of her children to suffer, Astra decided to give both of them the wand and crown. No succession crisis occurred, as the two decided that, whomever had kids first, that child gets the throne, which in this case was Heliador's daughter Oneira.
• Signverse AU: Andromeda and Orion both get wands on their 14th birthday, and both will inherit the throne when they're older.

Films — Animation

• Brave: In the backstory, there used to be an ancient kingdom, where the king decided to split the kingdom's rule between his four sons, believing that their unity would make their kingdom stronger. Unfortunately, the eldest son didn't agree with his father's vision and wanted the throne all to himself, which escalated to civil war, the collapse of the kingdom, and the eldest son's transformation into Mor'du.

Literature

• The Chronicles of Narnia: The four Pevensie siblings are crowned Kings and Queens of Narnia at the end of The Lion, the Witch, and the Wardrobe. We briefly get to see them working together in this capacity in The Horse and His Boy. The first-born Peter gets the title of "High King". Lampshaded in the film adaptation of Prince Caspian:
  Miraz: Tell me, Prince Edmund—
  Edmund: King.
  Miraz: I'm sorry?
  Edmund: It's "King Edmund," actually. Just "King" though, Peter's the High King. Yeah, I know, it's confusing.
• Chronicles of the Kencyrath: The twins Essien and Essiar share the title of Lord Edirr. This is standard practice in their House, which runs strongly to twins. Their heirs are briefly introduced, and are another set of twin boys.
• Earth's Children: Amongst the Mamutoi, Camps are led by a headman and headwoman, who are traditionally a brother and sister. The siblings Talut and Tulie are the co-leaders of the Lion Camp, while Tulie's eldest son Tarneg and eldest daughter Deegie intend to start up a new camp with them as the leaders.
• The Jewel Kingdom: Siblings in the original, cousins in the reprint. While the king and queen are still in charge, they give the four principalities surrounding the capital to the four Jewel Princesses.
• Kushiel's Legacy: In Kushiel's Dart, the throne of the Dalriada people is held jointly by twins Eamonn and Grainne, which poses some difficulty for Phèdre's diplomatic mission as she has to get both of them to agree to help her and Eamonn is a lot more cautious than his sister.
• The Locked Tomb: Gideon the Ninth: The position of Necromancer Heir to the Third House is held jointly by the Tridentarius twin sisters at their insistence, as is their Cavalier, contrary to tradition. It's a ploy by the twins to hide that the Red Oni older sister is actually a Muggle Born of Mages.
• The Lord of the Rings: In the backstory (detailed in The Silmarillion and the Appendixes), the brothers Isildur and Anarion founded the kingdom of Gondor together and ruled it as equals. Once reunited with their father Elendil who had founded the kingdom of Arnor they recognized him as their liege but stayed kings. After the War of the Last Alliance, Anarion and Elendil were dead so Isildur decided his descendants would be kings of Arnor and Anarion's those of Gondor. This mostly settled any legacy issues until Gondor ended up without a king and Arnor was destroyed leading the heir of Isildur (Arvedui) to try to claim the crown of Gondor and be rebuked as Gondor (eventually) settled on having a Steward instead of a king until the events of The Lord of the Rings.
• Once Upon a Marigold: Two of Marigold's sisters are married to the twin princes of a neighboring kingdom. The midwife lost track of which brother is older, so it has been decided that they'll rule jointly once their father dies. Then it turns out that Christian is their older brother, making him the sole king once their father dies. Olympia, who wanted to be the mother of as many queens as possible, is pretty upset about this development.
• Shades of Magic: White London is ruled by twin siblings Astrid and Athos Dane. They got the throne not by right of primogeniture, but by killing the previous king.
• A Song of Ice and Fire:
  • There are two in-universe historical figures named Gendel and Gorne who were brothers that shared the title of King-Beyond-the-Wall. Succession was not a concern because their people, the Free Folk, do not use inherited power and just follow the strongest warriors. They led a failed invasion into the North, only to be stopped by the King in the North and his son. It's known for certain that Gorne was killed in battle, but the Northmen and the Free Folk disagree on whether Gendel was killed as well, with the Free Folk believing he managed to escape.
  • Downplayed in the case of the Hands of the King. While Westeros uses a simple monarchy by default, there is a long tradition of kings naming close relatives to the position of Hand of the King, who serves both as a close advisor and who can exercise functionally all of the king's powers in absentia — the Hand speaks with the king's voice, commands the king's armies, and drafts the king's laws, and many Hands can and have acted as the realm's actual ruler when the king was weak or away. The tradition began with the first King Aegon, who named his bastard half-brother Orys as the first Hand; later examples included King Aenys, who named his half-brother Maegor as Hand; and Aegon III, whose Hand was his brother Viserys. Other cases saw kings selecting their uncles, sons, or nephews to this position.
• A Tale Dark And Grimm: The first book ends with Hansel and Gretel being crowned the new King and Queen of Grimm. Their mother quickly adds that they'll be marrying other people, just in case anyone was confused. Played With in the sequel, where the cousins Jack and Jill get the throne of Märchen.

Live-Action TV

• Foundation (2021) is a sci-fi variant: the Empire is ruled by three clones of Emperor Cleon I, referred to as Brother Dawn, Brother Day, and Brother Dusk in ascending order of age. A new Brother Dawn is decanted when the current Brother Dusk dies. They usually refer to one another as "brothers", but Cleon XIII confesses that he thinks of Cleon XIV as more of a son due to their significant age gap.
• Pair of Kings: The twins Brady and Boomer discover they're the heirs to the throne of an island called Kinkow, and they share the throne. (This is because no one but their mother knows which brother was born first, and she never told anyone before passing.) When Brady eventually decides to move back home to Chicago, Boomer meets his triplet, Boz, who ended up on a different island. From then on, it's Boomer and Boz who share the throne instead.
• The Quest: In the Disney+ revival, this ends up being how the succession crisis is resolved between the three heirs of Sanctum. Princes Cederic and Emmett and princess Adaline were gifted to the king as infants by the Fates, so there is no clear order of succession. Each of them has their own strengths that would make them a good ruler, but also flaws that would make them less fit to handle certain situations than their siblings. By the end of the series, each sibling has had a chance to realize this, so the Divine Crown gets split into three parts, with rule of Sanctum being shared equally between them.

Myths & Religion

• Arthurian Legend: The earliest version of Arthur being taken to Avalon has it ruled by nine benevolent fairy sisters, with Morgan le Fay being the most prominent. This was before she was reworked into Arthur's evil human sister.
• Classical Mythology:
  • Zeus and Hera are siblings and the Ruling Couple of the gods.
  • Several stories involve a pair of brothers taking turns in ruling their city one year at a time. Surprise, surprise, one brother decides he'd rather hold on to the throne and exiles his brother, who is usually avenged by his son.

Tabletop Games

• Pathfinder: King Noleski Surtova of Brevoy is a bachelor with no children, and his sister Natala consequently has a considerable amount of political influence — she's Brevoy's queen in all but name. Noleski has, however, begun to obsess over marrying. Natala is less than happy about this, as her brother finding an official queen could easily cost her her current power.

Video Games

• Crusader Kings: Gavelkind succession is meant to reflect traditions in many cultures that a ruler's lands would be divided between his inheritors, who would rule as equals.
• Final Fantasy VI: During the gameplay, it is revealed that Edgar and Sabin were meant to be this according to their father's dying wish, but later got separated after their fateful coin toss. Edgar stayed behind and became king, while Sabin remained prince and went to train in the mountains.
• Fire Emblem Warriors: This is the solution to the Succession Crisis. The twins Rowan and Lianna, neither of whom initially wants the throne, undergo Character Development and decide to jointly rule Aytolis.
• Pokémon Black and White: According to legend, Unova was founded and ruled by twin brothers with their legendary dragon Pokemon. However, they ended up having a fallout over truth and ideals, which resulted in the dragon splitting into three beings due to the division: Reshiram personifying truth, Zekrom personifying ideals, and what was left becoming the husk-like Kyurem.
• Warframe: The Grineer are ruled by the Twin Queens, actually Orokin who were mistreated for being identical twins and thus too similar to the cloned Grineer slaves.

Western Animation

• Care Bears (1980s): In one episode, Cheer Bear and Treat Heart play radically different sisters and princesses who are sent on The Quest by their father (played by Braveheart) to see who eventually gets to be queen. Since they end up working together and getting the Mineral Macguffin together, they come back telling their father, "Since we make such a good team, we'll both rule!" Their father's perfectly fine with that, making you wonder why he didn't just do that in the first place.
• The Legend of Korra: After their father Chief Unalaq dies in the Season 2 finale, Half-Identical Twins Desna and Eska both become equal "Chiefs of the Northern Water Tribe."
• Loonatics Unleashed: The Loonatics learn that Zadavia came to Acmetropolis as a refugee from planet Freleng, where she once held the throne along with her brother Optimatus. Optimatus, however, developed a bent for conquest and became an Arc Villain in the series. In the finale, Optimatus is betrayed by one of his accomplices, and decides to Set Right What Once Went Wrong. Zadavia and Optimatus reconcile and return to Freleng together.
• My Little Pony: Friendship Is Magic: The sisters Celestia and Luna rule Equestria as equal princesses. Although Celestia begins the series as Equestria's sole authority, due to Luna having become evil (in large part due to bitter jealousy over how their subjects seemed to love Celestia better), trying to stage a coup and being sealed in the moon for a thousand years, Celestia readily welcomes her sister back at the end of the show's pilot episode, and the two thereafter share rule and responsibility — the show's later seasons' episodes show them having paired thrones in their castle's throne room, for instance. Their reconciliation is not without its hitches, and a few episodes are dedicated to exploring lingering tensions between the royal sisters.
• Sonic Underground: Sonic, Sonia, and Manic apparently plan to share the throne after Robotnik attempts to sow discord amongst the trio over who has the Right of Succession to the throne. In a separate episode dealing with an alternate universe where everyone's morality is flipped, the three evil versions of the hedgehogs even do share power between them.

Real Life

• The Roman Empire frequently split the imperial throne between two or more co-emperors, more than a few were brothers.
  • Marcus Aurelius was co-emperor with his adoptive brother Lucius Verus until the latter died of either food poisoning or smallpox. He'd later appoint his son Commodus as a new co-emperor three years before his death.
  • Septimius Severus intended his sons Caracalla (already co-emperor) and Geta to be co-rulers after his death, however, this backfired horribly as the two hated each other and even considered splitting the empire in half. Their mother attempted to get the two to reconcile, only for Caracalla to have his brother assassinated in front of her, Un-person Geta, and rule as sole emperor until his own assassination.
  • Theodosius I, the last ruler of the united empire, gave the Eastern half (aka the Byzantine Empire) to his eldest son Arcadius and the West to his other son Honorius.
  • Half-brothers Constantine III and Heraklonas reigned as co-emperors after their father's death for four months before Constantine died of tuberculosis, and a rumor that Heraklonas' mother poisoned him got him deposed.
• It was traditional among the Germanic tribes that a leader's children would each get a piece of the kingdom and rule as equals. Part of the chain of events that led to the Frankish king Charlemagne being crowned Roman Emperor was him seizing his brother Carloman's former lands from his young nephews after Carloman's sudden death. King Desiderius of the Lombards, enraged at Charlemagne divorcing his daughter, supported the claim of Carloman's children. In response, Charlemagne invaded and conquered the Lombards with the backing of the Pope.
  • The issues involving this trope, among other things resulting in the Empire splitting into what is now France and Germany, is what led Hugh Capet to crown his oldest son Robert King of France while Hugh was still alive and having him co-rule with his father: a kingdom can't be inherited if one of the kings is still alive, after all.
• Attila the Hun and his brother Bleda were co-rulers of the Hunnic Empire until Bleda's death, which some historians say was Attila's doing.
• Coregency happened exactly once in the history of Tsarist Russia: After the death of Tsar Feodor III, his brother Ivan V and half-brother Peter were both crowned "autocrats of Russia," though because neither was of age to rule yet, Ivan's older sister Sofia claimed regency in the meantime. The whole two Tsars thing only happened as a compromise to avoid a civil war of succession because Ivan was sickly and unable to rule, whereas Peter, while the next in line, was vehemently opposed by Sofia. To his credit, even after removing Sofia from power, Peter continued to honor the arrangement, deferring formal seniority to Ivan until the latter's death of natural causes almost two decades later. It has also been speculated by historians that this coregency was what paved the way for Peter's massive reforms: since there was already a Tsar in Moscow (Ivan), the other Tsar was free to travel Western Europe (and boy, did Peter ever) and to learn how things were done in other countries first-hand without worrying too much about the situation at home.

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