Historians at Ancestry.com have traced the Fanning family history back hundreds of years and discovered Super 8 star Elle is the 22nd great-granddaughter of England's King Edward Iii, who ruled from 1330 to 1376.
That means Dakota is also a descendant of Edward Iii through their mother, Heather Joy Arrington.
Ancestry.com's Michelle Ercanbrack tells People.com, "Generation after generation, the lines we looked at pieced back directly to King Edward Iii proving that Elle is a direct descendant of royalty.
"You can consider her a long lost princess. This connection is so unique and rare."
Website experts have also established the Fannings are distant cousins of Prince William's wife, Catherine, as the Duchess' mother Carole Goldsmith is also a descendant of King Edward Iii.
Ironically, Elle Fanning plays Disney princess Aurora in new movie Maleficent.