Fanfic writers aren't the only ones who do it. I have to laugh at The Tudors and The Other Boleyn Girl, because by the time Henry VIII got around to marrying Anne, he had been married to Catherine for 20+ years before the divorce, and was already starting to put on weight. Catherine was the only one, pretty much, who got to sleep with him when he was slender. But nooooo ... we have to have a "hot" Henry. You can see how attitudes have changed, too: the early 1970s Masterpiece Theater production distinctly shows Henry's physical decline - but then again, they're not romanticizing him.