Paul Adelstein is also on board for the special two-hour episode

Tim Daly is the latest actor cast in the two-hour "Grey's Anatomy" episode that may become a spinoff from the smash ABC hit.

In addition, in a move sure to please "Grey's Anatomy" trivia buffs (but concern "Prison Break" fans), Paul Adelstein will appear in the potential spinoff episode.

Both actors join Taye Diggs in the episode, which will focus on Kate Walsh's Dr. Addison Montgomery.

Series creator Shonda Rhimes is writing the episode, which -- like every other episode of the ABC hit -- is shrouded in mystery. All that's known is that the two hours will present Addison with a situation that could find her leaving Seattle Grace.

According to The Hollywood Reporter, Daly will play a character described as "handsome, sincere, like a McDreamy."

The trade paper has no info on what role Adelstein will play in the episode, but since the "Prison Break" co-star (he plays Kellerman) was originally cast as Dr. Burke in the "Anatomy" pilot, fans are sure to be enthusiastic.

Daly has had a busy, but not entirely successful relationship with ABC in recent years. The "Wings" and "Diner" star has been featured in the dramas "Eyes" and "The Nine," which both earned strong reviews and very short runs.