Right, but I’m still leaning toward Amie being his daughter. It’s too weird a coincidence to have a completely unrelated Piers Gaveston having a daughter at the same time our Piers was running around and giving her the same (fairly uncommon name) as our Piers’ sister.
I don’t think there’s really any good evidence for her being his wife’s illegitimate daughter, when the contemporary records refer to her as being “Piers Gaveston’s natural daughter”. How would that work, anyway? His wife hides the pregnancy from him and gives birth without him noticing and makes sure nobody tells him? Or she doesn’t, admits she cheated on him, and in a remarkably generous and uncharacteristic moment for the prickly, vain and jealous Gaveston, says says, “That’s ok. I’m not mad. And in spite of the fact that we could pretend the kid is legitimate, we’ll just keep her a secret.”
That’s why I think the “It’s his wife’s illegitimate daughter” is the least likely of all, and comes, I think, from the stereotype of “Gaveston had a homosexual relationship with Edward, so therefore he can’t have had a mistress.”, which is right up there with the “Piers Gaveston was effeminate and girly” thing you see trotted out by some people.
If Amie was Margaret de Clare’s illegitimate daughter, she was almost certainly born after Piers’ death. If she’d been born during their marriage, she would’ve been considered legitimate, regardless of her actual paternity, and would’ve been their heir after Joan Gaveston’s death. Also, the record identifying Amie does NOT call her “Piers’ natural daughter” – it says, in Latin of course, “Amie, daughter Petrus Gaveston.”
My problem with Amie being Piers’ daughter is that she was called a ‘maiden’ in a rather late record, then went onto marry and have children. Women in this time period tended to marry between the ages of 12-18, not in their late twenties or early thirties. It makes me suspicious that she might’ve been born several years after his death and called Gaveston out of courtesy.