Shar Jackson, Kevin Federline Celebrity Fit ClubDuring an emotional episode of 'Celebrity Fit Club,' Kevin Federline finally apologized to Shar Jackson for cheating and leaving her to be with Britney Spears.

"I know I've caused you a lot of pain. I've been selfish. I guess I got so wrapped up in all this other s**t that I never really sat back and got the chance to apologize to you," Federline started. "I am sorry."

Watch the full apology (forward to 4:10):