Aaron: God? When did God start caring about any of us? In fact Moses, when did you start caring about slaves? Was it when you found out you were one of us?
Let's say Bob is fighting a long-hated group of the side he was raised by. No tales of being affiliated with them at all in his youth or information of his origins. Now consider that Bob has just found out he is one of group he has fought against for so long. Bob decides to defect and join the side he has been fighting against. That is essentially this trope.
This is a circumstance where a character decides to make a HeelFace Turn or FaceHeel Turn to a side that they once denigrated, oppressed, or fought against because of the revelation that the character is actually a member of the side by birth or by heritage.
This kind of situation can be seen in stories as result from the factor of there being a HeelFace Turn but keep in mind that the side an example portrays is not always malevolent or benevolent. This trope tends to happen to characters who were Raised by Natives or Raised by Orcs, more often than not the consequence of a Child of Two Worlds.
- On the Dirty Pair light novels, the galaxy-wide criminal conspiracy "Lucifer" had one particular method to make sure that all of its members were fanatically loyal: they were ALL related by blood. A few of the times that it appeared on the novels, such, all they had to do was drop the "Luke, I Am Your Father" card on the Victim of the Week to make them despair about whether or not to join (and some did).
- In Wolf's Rain, Blue hunted wolves along with her master for most of her life until she learned she was half-wolf. She then joined the wolves out of disgust.
- In Age of Bronze, the High King of Mysia Telephus breaks off hostilities and joins with King of Rhodes Tlepolemus to provide supplies for the Achaean fleet against the Trojans when he discovers they're both sons of Herakles despite Tlepolemus' forces killing hundreds of his men a short time before the revelation. However, he refuses to have his men join the fleet because his wife was one of the daughters of the Trojan King.
- In The Prince of Egypt, Moses finds out about his Hebrew heritage from his sister, Miriam, and decides to leave the comforts of his Egyptian upbringing as penance for the acts of genocide and slavery committed by the Egyptians against the Hebrews and to free them on the order of the Abrahamic God of the Hebrew People.
- In Ilya Muromets, the titular hero is dueling with a young enemy warrior, and suddenly notices the boy is wearing a ring he gave his wife, making him realize he is fighting his own son. The boy is skeptical, but once he looks at the ring, he remembers his mother and says at once he wants to fight on Ilya's side.
- Star Wars: In the original trilogy — specifically in The Empire Strikes Back and Return of the Jedi — this trope is invoked and averted when Darth Vader attempts to goad his son Luke Skywalker into joining him and the Sith in the in the infamous "I am your father" scene. It is then defied by Luke throughout the rest of the trilogy — despite Luke fully acknowledging Vader as his father, he has no intention of joining him in ruling The Empire.
- An inverted case for Loki in the film Thor. Loki finds out he is of Jotunn — Frost Giant — lineage and confronts his adoptive father Odin who reveals he adopted an abandoned baby Loki after his forces killed many of the Frost Giants. Angered at being the unfavorite and by the revelation that Odin took Loki in an attempt to use him to bring about an alliance and permanent peace between the Asgardian and Jotunn kingdoms, he decides to betray Odin and the Asgardians. However, he does so by attempting to annihilate all the Frost Giants, decrying them as a race of monsters, to prove himself worthy of being the King of Asgard.
- In Dan and Mab's Furry Adventures, Daniel Ti'Fiona lived his early life as an adventurer: going on quests, chasing skirts, and fighting monsters such as cubi along the way. He later discovers his mother was a succubus named Destania, which means Dan is a cubi of clan Cyra. He didn't take this news well at first, but it grew on him while he attended the Succubus And Incubus Academy until he grew to accept this part of himself and the cubi.
- In the Castlevania series, an averted case is present for Alucard, the dhampir son of Dracula with a human female. Alucard has a great affection for humanity, and fights against his father because of the monster he is. Despite his real name being Adrian Farenheights Tepes, he adopted the moniker of "Alucard" (Dracula spelled backwards) to demonstrate his opposition to his father despite his own vampiric heritage.
- In Fire Emblem Fates, it is revealed early in the story that the Player Character, who grew up in Nohr, was actually kidnapped from Hoshido as a small child. A war breaks out between Hoshido and Nohr soon after. The Birthright route has the Player Character side with their native Hoshidan family, whose members they haven't known for very long at that point. The Conquest route has them side with Nohr instead, subverting this trope.
- In I Have No Mouth and I Must Scream, Nimdok's story involves him facing the fact that he was a Nazi scientist and Josef Mengele's partner as part of an experiment to create a Youth Serum created via the deaths of countless Jewish children after the Nazi Party fell. Horrified, Nimdok tries to atone by stopping the experiment and freeing the Jewish prisoners, but later finds out he was actually a Jewish scientist who betrayed his parents to the camps during World War 2 and worked for Dr. Mengele. In the end, Mimdok decides to repent and side with the escaped Jewish prisoners who decide to kill him for all the prisoners he had experimented on.
- In Resident Evil 6, an averted case is present for Jake Muller, a mercenary that entered into the business to financially support his mother since his father abandoned them when Jake was a child. During the game, there's the revelation that "Muller" is the last name of his mother and his father was none otherthan the deceased Big Bad of the series: Albert Wesker, explaining his general immunity to the Umbrella viruses and possession of the good properties of them like Wesker. After uncovering his paternity, Jake still keep going as an ally to Leon Kennedy and Chris Redfield during the game and decries his relations to his father.
- In the Gravity Falls episode "Northwest Mansion Mystery", Pacifica learns that her family has consisted of a long line of cheats, cutthroats, robbers and other criminals. Disgusted, she resolves to break away from that pattern, starting by letting in the townspeople into the Northwest mansion in order to break the ghost's curse.
- In The Secret Saturdays, the secondary antagonist henchman Doyle is discovered by Drew Saturday to be her long lost brother. As a result, he soon joins Team Saturday and helps them in their adventures.
- Learning He-Man is her brother is the final factor forcing Adora's HeelFace Turn in She-Ra: Princess of Power.
- In Teenage Mutant Ninja Turtles (2012), Oroku Saki later known as the Shredder proved to be an example. He was born from the Foot Clan but discovered by the father of Hamato Yoshi alone as a baby after a particularly devastating assault by the Hamato Clan on a Foot Clan village, before being raised alongside Yoshi, completely unaware of his heritage. However, after having a falling out with Yoshi after fighting and losing for the love of their mutual love interest, Oroku fled and eventually learned of his true heritage, choosing to rebuild the Foot Clan and donned the moniker 'Shredder' to take revenge against Yoshi and the Hamato Clan.