Although the plot is still shrouded in Shonda Rhimes-style secrecy, both TV Guide and Variety magazine have discovered some new dirt on the planned Grey's Anatomy spin-off, and how it may begin.

Variety says that "My Favorite Mistake," a two-hour Grey's Anatomy episode setting up an Addison Montgomery (Kate Walsh) spin-off, is scheduled to air this spring.

In addition to opening the door for Addison to possibly leave the halls of Seattle Grace, "My Favorite Mistake" will also introduce guest star Taye Diggs - as well as Hector Elizondo (Chicago Hope) as Callie's father.

The episode will be directed by Michael Grossman, who was last behind the camera for "Great Expectations" - the terrific episode in which both Burke and George popped the question to their respective ladies.

An exact air date for "My Favorite Mistake" has not been announced by ABC, but the episode will serve as the 22nd and 23rd Grey's Anatomy episodes (out of 24) in the current Season 3.

This is all very interesting news. Is the door also open for Addison to remain at Seattle Grace if viewer response to the episode is negative? Or is it a done deal that she's gone? Previous reports suggest the latter, but this makes it sound slightly less certain.

In any event, Grey's Anatomy returns with new episodes in two weeks, Thursday, March 15. That episode will be titled "Scars and Souvenirs."

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.