The much awaited Grey's Anatomy and Private Practice cross-over episode will be on air today in the United States. The cross-over episode will focus on the reunion between the Sheperd siblings, who are both nuerosurgeons.

Fans will get to pick what makes Derek Sheperd tick over his father's murder as his sister Amelia visits Seattle Grace. Caterina Scorsone will finally be able to meet her on-screen big brother Patrick Dempsey (who plays Dr. Derek Sheperd) who said that they "look like [they] could come from the same mother and father."

Previously, Caterina Scorsone revealed that the estranged siblings would reunite, thanks largely to the prodding of Derek's ex-wife Addison!

"Basically, Addison kicks her in the keester," Scorsone told E! Online.

"Amelia is kicking and screaming and doing everything she can do to avoid the inevitable, but Addison somehow convinces her that she's gotta go to Seattle." So...blame Addison. Or rather, thank her."

According to Scorsone, the two neurosurgeons had a falling out after the death of their father, who was previously revealed to had been killed in a robbery (Remember that eerie episode featuring criminal in a death row, who slit women's throat?).

The cross-over episode promises to reveal more insights on Dr. Derek Sheperd, and fans might now know why Dr. McDreamy's eyes are at times, so sad. Find out more today as the cross-episode airs in the United States!