AceShowbiz -

As "Grey's Anatomy" enters the sixth season later this fall, there might be one character noticeably missing from the line-up. Sources are telling E! News' Marc Malkin that T.R. Knight will not be back to the show after his rift with creator Shonda Rhimes became too "unbearable for both".

The root of the departure dated back when T.R. complained on the creative direction of his character, George O'Malley. The actor thought George had less screen time and lacked a story line. Therefore he wanted to be detached from the contract so that he can pursue other things. Rhimes herself refused to be explicit about the issue, simply saying "I think that there have been lots of rumors about TR, but TR's never said anything. Take from it what you will."

On the season 5 finale that aired earlier this month, George shocked Bailey and the rest of the crew when he wanted to join U.S. army as a trauma surgeon. However, in a twist of fate, he was struck by a bus while trying to save a woman from being hit. He flat-lined toward the end of the episode, joined by Izzie who also lost the sign of life.

Nothing was addressed about Katherine Heigl, who has submitted her name back as an Emmy Awards contender for her portrayal of Izzie.