Credit: Jason Merritt/Getty Images; Michael Buckner/Getty Images

Glee's Dianna Agron didn't exactly sing a wistful ballad following her split from actor Alex Pettyfer after nearly a year together.

Since moving out of the L.A. home she and the I Am Number Four star shared about two weeks ago, Agron, 24, "is staying at a hotel under an alias" a source reveals in the new Us Weekly, out Wednesday.

Why the secrecy? Pettyfer, 20, has been "a psycho loose cannon" in the aftermath of the split, another insider says.

On Feb. 18, according to an eyewitness, he got into a heated confrontation at a West Hollywood club with actor Sebastian Stan -- furiously accusing the Black Swan star of hooking up with Agron.

"Dianna is terrified of [Alex]," a pal explains, adding that he "absolutely lost it" and threatened Agron during a vicious phone chat. (Pettyfer's rep tells Us he made no threats.)

To read much more about the ugly breakup, pick up the new Us Weekly, out Wednesday.