Miley Cyrus Single Again.

Now that Miley Cyrus is a single lady again, let the

speculation begin about what caused her split from boyfriend and former The Last Song co-star Liam Hemsworth.

According to E!'s Ted Casablanca, 17-year-old Miley (understandably) isn't ready to "settle down" with her 20-year-old beau, who she called her first serious boyfriend. (Sorry Justin Gaston!)

"Miley has been super focused on her work," an "insider" tells E!. "Liam wanted more, but she's 17 and has other priorities right now. He's been a distraction."

The pesky rumor mill has already begun churning, saying Miley's eye wandered to her LOL co-star Adam Sevani, with whom she has been hanging on the Detroit movie set. But according to Casablanca,

"Miley'snot with anybody else."

In a sad twist of fate, The Last Song, the movie on which Miley and Liam met and fell for each other, is killing it in new DVD sales, according to theHollywood Reporter.