It's like the first day of school as Caterina Scorsone hits the set of Grey's Anatomy. She's there to begin filming the big Grey's-Private Practice crossover. Bubbly and bright-eyed, the new girl roams the halls of Seattle Grace with a sense of awe.

"No matter what, when you start a new situation like that, especially with these people that you've loved and admired for so long, you're going to be nerve-wracked," Scorsone tells TVGuide.com.

Her arrival is the moment Grey's fans have been waiting for since Scorsone joined Private Practice as Derek Shepherd's estranged sister Amelia. In Thursday's episode, Amelia will come back into Derek's life, opening up old wounds and shedding new light on McDreamy's past.