Books that started as fan fic?

This is sort of a request post but also sort of a "just for fun" post...my husband and I were talking about how there seem to be quite a few published mf books recently that started out as fan fic (I'm reading an ARC right now for a book called "Rose in Chains" that fits this, but was also thinking of "Ministry of Time," "The Idea of You," etc.) and I was wondering which mm books out there started as fan fic? The only ones I could think of off the top of my head were the Rainbow Rowell Simon Snow series (Harry Potter), Vanora Lawless's "Imperfect Illusions" and the sequels (Stucky), and another Stucky AU-inspired book, which I love but can't mention here because one of the characters is under 17 when the book starts. 🤐

So I'm wondering...which other ones are out there?

ETA: Just remembered "A Land So Wild," which is based on a Johnlock fic.