Yes, 'Red White and Royal Blue' started out as fanfiction. Fanfiction writers take existing universes or characters and create their own stories. This particular work, which grew out of that fan - based creative space, has since become a well - known story in its own right. It has been able to build on the initial fan - created ideas and expand into a full - fledged novel and subsequent adaptations. The fact that it began as fanfiction also means it has a unique origin story compared to works that are created entirely independently.
Yes. Many people might not be aware, but 'Red White and Royal Blue' has its roots as a fanfic. Fanfics are often a creative starting point for many works, and this one managed to gain enough popularity and was developed further into the story we now know, with its own unique plot and characters that have attracted a wide readership.
I don't know, to be honest. It could be an original story that just shares some common themes or tropes with other works, but not directly a fanfic of something specific.