Warner Bros.

Ah, "OC" memories.

Kaley Cuoco is out at "Grey's Anatomy," and Shannon Lucio is in. "Big Bang Theory" actress Kaley, who earlier this week announced she'd be appearing in the "Grey's" finale in a top secret capacity, has had to pull out of the gig due to an unforeseen "publicity commitment," according to Entertainment Weekly. They report that "OC" star Shannon Lucio will be filling in.

On "The OC," Shannon, 28, played Caleb Nichol's illegitimate daughter Lindsay (we're sure she's a lovely woman, but she definitely didn't win us over with that Ryan/Marissa-separating role). She's also starred on "Prison Break," and AMAZING movie of the week, "Spring Break Shark Attack."

Now for the fun part -- what in the world is this mysterious "Grey's" part? Is it a patient-of-the-week thing, or something bigger? Like -- another Grey, in town for the big Mer/McDreamy wedding! Or an Izzie sister, come to help her through the cancer?

Give us your best guess, in the comments below!