On March 22 1917, Tzar Nicholas II was placed under house arrest with his family by the Provisional Government. Then, on July 17 1918, they were killed by Bolshevik troops led by Yakov Yurovsky. However, rumors began to spread that the youngest daughter, Anastasia, survived. This led to several women coming forward and claiming to be the grand duchess. The most famous of these was Anna Anderson, who had previously been institutionalized in a mental hospital. Her story later inspired a French playwright named Marcelle Maurette to write a play titled Anastasia. Then, an Anglo-American playwright named Guy Bolton adapted the play into English. In 1956, 20th Century Fox adapted the play into a film starring Ingrid Bergman as Anastasia. Finally, in 1997, the movie was adapted into an animated film by Don Bluth, who added Disney tropes and a tacked-on villain. And now there's also a Broadway musical based on the animated film, which will no doubt be itself adapted into another live-action film down the line.
TL;DR - This movie is an adaptation of an adaptation of an adaptation of an adaptation of a real-life story where a woman pretended to be dead royalty. The Anastasia story has basically turned into a tall tale.
Golden Anastasia and Rambo III suck too.