ET has the details...

This just in -- ET breaks the news that "Hannah Montana" herself, MILEY CYRUS, has legally changed her name! The teen superstar has changed her name to Miley Ray Cyrus, making her nickname, "Miley," official and adding the middle name of her dad, country music star BILLY RAY CYRUS.

The 15-year-old, whose birth name was "Destiny Hope Cyrus," tells our JANN CARL that she has always been called "Miley" by family and friends, so she wanted that to be her legal name, and chose "Ray" as her middle name because she wanted the same one as her dad.