Katherine Heigl has often called her "Grey's Anatomy" co-star T.R. Knight her "best friend." Now, Katherine can call him something else: Bridesman!

Us Weekly is reporting that T.R. will be in Katherine's wedding party when she ties the knot with musician Josh Kelley.

"I'm standing up there and all, so I have to go and get the tux," T.R. told the mag. "And I am still deciding on a gift!"