Irish American actress Mandy Moore is to appear on the final episode of this season's "Grey's Anatomy."

The folks at Seattle Grace go off our screens in a two-hour finale on Thursday, May 20 on ABC.

Producers call the show "a real shocker."

Now that we know Moore is going to be in it - as a patient - we are going to be glued to our television sets here at

The finale will be called "Sanctuary"

Seattle Grace is going to be hit "with a crisis like no other," said producers.

Moore will play a patient called Mary. She will be treated by Bailey (Chandra Wilson)

Mary's husband will be played by Ryan Devlin - of "Veronica Mars."

High intense drama in the finale episode will find Dr. Meredith Grey and her friend Dr. Christian Yang using their surgical skills like never before.

This is one not to be missed.