Where has Aaron Carter, ex-boyfriend of Hilary Duff and Lindsay Lohan, and little brother of Backstreet Boy Nick Carter, been lately?

He's at his manager's compound "working on my mind, music, and body for a new album release," according to a recent tweet he posted along with a new shirtless photo of his startlingly buff bod.

Sharing his fitness routine in another early-morning tweet, Carter says, "ahhhh yawn....here i go again!!!! 1000 pull ups today 7 mile run 1000 sit ups, i can't stop myself 5:00a.m."

He even added another pic of his abs for good measure, after declaring to his followers: "In the process of developing a new style of dance. This will be unforgettable."

The 22-year-old, who has a twin sister, followed in big bro Nick's footsteps by recording pop music in the late '90s; his 2000 release 'Aaron's Party (Come Get it)' went triple platinum.