Jenny: I'm a mama... his name's Forrest.
Forrest: Like me.
Jenny: I named him after his daddy.
Forrest: He's got a daddy named Forrest too?
Jenny: You're his daddy, Forrest.
A man's girlfriend leaves him and marries someone else. She and her new husband have a son together. The man, jealous, develops feelings of resentment and even hatred towards the boy, whom he believes to be the offspring of the woman he loves by another man. When they meet, the relationship between them is tense at best, homicidal at worst.
Then one day someone reveals the truth. The man was the child's father all along! He's spent years resenting someone who was in fact his own son!
This is a common variation on the Your Son All Along trope. This trope covers any situation where a man believes that a child is his love-interest's by another man, then discovers that he is in fact the true father. Basically, it's the inverse of cuckolding.
For obvious reasons, the parent in these stories is almost always male. For less obvious reasons, the child is usually male, too. In many cases there is an adversarial relationship between parent and child prior to the revelation, but not always.
Sub-trope of Luke, You Are My Father and Mama's Baby, Papa's Maybe. The distinguishing feature is that the parent originally believes the child is someone else's, and only discovers the truth later - sometimes not till after the child is dead! This is significant because in most examples of Luke, You Are My Father, the surprise comes from the man learning that he is a parent, with the potential responsibilities that that entails. In this trope, the surprise comes from the man learning that he is the parent of a particular child. This forces him to rethink his relationship with that child and also, potentially, with the child's mother.
As this is a form of The Reveal, unmarked spoilers abound. Beware.
- Usagi Yojimbo has a variation in that Usagi knows Jotaro is his son, and Jotaro knows Usagi is his father, but neither knows the other knows and go to some lengths to hide it. The only time it's revealed is in the Else World "Senso", where Jotaro calls a dying Usagi "Father" and Usagi is astonished that Jotaro knew all along.
- Indiana Jones and the Kingdom of the Crystal Skull has Indy finding out that Mutt is his son.
- Used tragically in the French duology Jean de Florette and Manon des Sources. In the first film, ''Jean de Florette', the protagonist wants the titular Jean to sell him his land, and plays many tricks on him to pursuade him to do so. It doesn't help that Jean is the son of his childhood sweetheart Florette, who left him and married another man while he was away at war. In the end, he successfully drives Jean to his death and takes the land. In the second film Jean's daughter, Manon, takes revenge for her father's death. It is only at the end of this film that the main character discovers that, contrary to what he thought, Jean was not Florette's son by her husband, but his own son, and that he has unwittingly caused the death of his only child and been in conflict with his granddaughter!
- No Time to Die: Just as James Bond is about to let himself die in the missile strike on the IslandBase at the end, Madeleine Swann tells him that Mathilde "does have [his] eyes", to which he answers "I know..." before perishing.]]
- Silent film West of Zanzibar, and its talking remake Kongo, both involve a Villain Protagonist whose wife cheats on him and leaves him for her lover, only to suffer a Death by Despair soon after and leave the husband with the daughter she conceived with the lover. The husband then sets out on a twisted Best Served Cold revenge plot which involves letting the daughter grow up, turning her into an alcoholic prostitute, and then presenting her to the Glorified Sperm Donor dad. This backfires spectacularly when the lover gleefully reveals to the husband that the young woman is actually the husband's daughter.
- The Amazing Adventures of Kavalier and Clay: Tommy's parentage, while known to the reader, was unknown to Joe until Rosa and Sam revealed the truth.
- Inverted in The Mayor of Casterbridge. Michael Henchard, the title character, drunkenly sells his wife Susan and infant daughter Elizabeth-Jane to a sailor, Richard Newson. Two decades later, Newson is lost at sea and Susan returns to Henchard, bringing Elizabeth-Jane along with her. It is only upon Susan's death that Henchard learns that Elizabeth-Jane is not the same child he gave up, but a different child fathered by Newson, Henchard's daughter having died a few months after the sale.
- The Thorn Birds turns it upside down in that, in this case, Ralph adores Dane from the moment he first sees him. He instead harbors some resentment towards Dane's mother Meggie, assuming that despite their passionate interlude (when Dane was conceived), she returned to her neglectful husband Luke.note It's only after Dane's death that Meggie reveals the truth to Ralph, who admits that deep down, he probably knew all along.
- Some adaptations of The Count of Monte Cristo add this trope (which was absent in the original novel) to make Dantes's last-second sparing of Albert de Morcerf all the more dramatic. In the original, all parties involved probably wish they were related, especially once the full extent of Albert's father's villainy is exposed.
- Annika (2021): Annika has a teenage daughter named Morgan, whom she reveals in the series 1 finale was fathered by her current Number Two Michael when they were dating at Police College. At the time she believed he wasn't mature enough to be a father, and didn't want the terrible relationship she has with her own father for Morgan. She spends the first two episodes of series 2 trying to tell Michael about it and getting repeatedly interrupted before she manages to spit it out at an open-mic night he tricked her into.
- In Dallas, both Sue Ellen and JR believed that her son was the result of an affair with Cliff Barnes, JR's arch-rival. When it's discovered that Cliff might have a hereditary condition that could be passed to offspring, it is found out that John Ross III was, in fact, JR's son.
- Inverted on Days of Our Lives. Craig is floored when wife Nancy confesses that she had a teenage daughter (Chloe) that she gave up for adoption. He asks her how she could hide the fact that "they" had a child together (they'd been childhood sweethearts but lost touch when he left for college, reuniting years later) and is devastated when she tells him the girl is her daughter, not his, meaning that she had cheated on him. After a rough start, the three are able to bond as a family. Then the girl becomes ill and needs a bone marrow transplant, at which point Nancy confesses that she's her Child by Rape. However, when the rapist's blood type doesn't match the girl's, Craig realizes that the young woman who he's grown to love as if she were his own daughter... is his daughter.
- In General Hospital, Alan and Monica spent several years believing that their son AJ was the result of Monica's affair, before finding out that he was Alan's son after all. Unfortunately, crucial bonding time had been lost between the two, resulting in years of AJ being The Unfavorite (compared to Jason, the son conceived during Alan's affair and adopted by Monica) and an alcoholic failure. Decades later, AJ (correctly) suspected that he was the father of Carly's unborn child, but she lied and told him that his brother Jason was, fearing that either AJ or her boyfriend Tony would take the child away from her. Years later, Jason's girlfriend Robin finally told AJ the truth.
- Hannibal: Veteran Serial Killer Lawrence Wells' first victim was his mistress's husband, and her last victim, forty years later, was her son. He intended it to be a final blow against the mistress, but has a Villainous BSoD when he learns that he, not her husband, was the true father.
Will: You thought the woman you loved was having Fletcher Marshall's baby when she should've been having yours, but you got it the wrong way around! Eleanor chose to raise him as Fletcher Marshall's child rather than yours... so, maybe, she saw what's in your heart.
- Law & Order: SVU: In one episode, a missing teen girl ends up being a runaway who was trying to start a new life with her music teacher, with whom she'd been having a relationship. Upon the reveal, the girl's mother insists he be jailed for incest, because the daughter is the result of a brief fling they'd had. The teacher is disgusted that he'd been sleeping with his own daughter, but the girl is blissfully happy with the reveal that her biological father isn't a garbage man like she'd always believed.
- My Name Is Earl: Joy believes that Li'l Chubby is Dodge's father, but she's afraid of him, because she witnessed him mistreating another woman who claimed to be pregnant with his child. Earl wants her to come forward to Chubby, because he can see that Dodge (and Earl Jr.) are suffering due to their living in Perpetual Poverty. Joy tells him to drop it, but he persists, and gets a Daddy DNA Test, against all odds (with a little help from Darnell). The test shows that Dodge is not Li'l Chubby's... but Earl's. As it turns out, Earl and Joy conceived him at a Halloween party, and did not recognize each other afterwards. For the six years that they were married, Earl had been led to believe that Dodge's biological father was a stranger from a concert. In another Ass Pull, the test also shows that Earl Jr. is not Darnell's, as previously thought. It's never stated who his father actually is, due to the series being canceled, though Word of God says it was supposed to be a celebrity.
- In the penultimate episode of The Office (US), Angela reveals to Dwight that he is the real father of her toddler son Phillip after he and Angela had one last fling a month before her wedding to the senator.
- Outlander: Brianna Randall Fraser is raped by pirate Stephen Bonnet on the same night that she and her fiancé Roger MacKenzie consensually had sex a few hours earlier, and when she becomes pregnant it's unclear which of them is the biological father of her son Jeremiah. It doesn't help that he turns out blond like Bonnet rather than redheaded like Bree or brunet like Roger. Regardless, Roger promises to raise Jemmy as his own son when he marries Bree. Later, Jemmy demonstrates stronger than usual time traveler abilities, suggesting that he was Roger's biological son all along since both Bree and Roger are time travelers, and this is cemented when he develops the same hereditary mole on his head as Roger.
- Scream Queens (2015): A DNA test proves that Weston Gardner is the father of Boone and Hester.
- In Scrubs, when Jordan becomes pregnant the first time, she claims that the father was a one-night stand, but is unclear which one. It is actually Dr. Cox's baby, but she doesn't tell him in order to hold their relationship together. Eventually it leaks to Dr. Cox that Jack is his son, at which point Dr. Cox is angry at Jordan for keeping it a secret from him.
- Shakespeare & Hathaway - Private Investigators: A Gender Flipped example in "Ill Met by Moonlight", Lady Bede had an Arranged Marriage that became a Sexless Marriage to escape her tyrannical parents. She was impregnated with her daughter by the gardener, who remained unsuspecting and worked with her family for years.
- In Love Never Dies, the Phantom realizes at the end of Act One that Gustave is his son, not Raoul's.
- At the end of Metal Gear Solid 4: Guns of the Patriots, in a Throw the Dog a Bone moment it's reveal that Rose's son is Raiden's (her marriage to Campbell was a sham to prevent the Patriots coming after the kid to get leverage over Raiden). The son then hammers it in by doing the same moves Raiden does with a toy sword.
- Devil May Cry 5: Heavily implied by several dialogue lines. In the Visions of V manga, Griffon speculates and tells V that Nero is a blood descendant of Sparda, either the child of Dante or Vergil. The game eventually confirmed the latter, and revealed V as the human half of Vergil. But because Vergil still needed Dante to spell it out for him in the end (as quoted below) in order to remember his visit to Fortuna from "a long time ago", this created the retroactive implication that V and Nero spent most of the game unaware that they are father and son. Likewise, Vergil was "preoccupied" as Nelo Angelo, so the only logical conclusion for him was that Nero is Dante's son.
Vergil: Nero is my son?
Dante: Yeah, dumbass. You can't remember through that thick skull of yours?
Vergil: Well, well... That was a long time ago.
- A rare female version can be found in Umineko: When They Cry when it's confirmed in Ep 8 that Battler's biological mother isn't Asumu but Kyrie. A baby switch was made by Rudolf when Asumu's child was a stillbirth, as he thought it would be easier since he and Asumu were married while Kyrie was a lover.
- Throughout the first half of The Venture Brothers, Dermott Fictel is assumed to be the illegitimate son of Brock Samson; but in Season 4 it's revealed he's actually the third Venture brother, and his mother isn't even his actual mother, but his grandmother.
- In The Angry Birds Movie 2, Zeta drops two bombshells in succession. First, she tells her ex-fiancé Mighty Eagle that Debbie is her daughter. As the main cast gasps in surprise, she then says, "Our daughter". This shocks everyone who hears this, especially Debbie and Mighty Eagle.
Debbie: That's my dad?
Mighty Eagle: I have a daughter?
- Prior to the start of DuckTales (2017), Scrooge's former spy partner showed up on his doorstep with a baby she claimed was her granddaughter and asking for a safe place to retire. Scrooge subsequently spent the next 10 years with Mrs. Beakley working as his housekeeper and her granddaughter Webby living in his house but didn't spend any time with her until his own family returned. After three seasons of Scrooge bonding and adventuring with Webby, they both learn she's actually his daughter secretly made by FOWL because Bradford needed an heir of Scrooge McDuck for his plan.