Watch: Patrick Dempsey and Kate Walsh's Surprise Reunion Will Give You 'Grey's Anatomy' Flashbacks

Just when you thought Dr. McDreamy was gone for good, he comes back with a surprise reunion.

Patrick Dempsey and Kate Walsh reunited for a brand-new ad campaign for Cigna. Joined by Neil Patrick Harris (Dr. Doogie Howser) and Donald Faison (Scrubs' Dr. Turk), the Hollywood doctors advocate the importance of yearly check-ups and preventative care.

"We're partnering with Cigna to remind you to go see a real doctor," Walsh shared in the ad. Dempsey added, "Go, know and take control of your life."

It has been almost five years since the Grey's Anatomy duo shared the small screen on the ABC hit series. However, it appears the two fell right back into old patterns when they worked together again.

"Kate's fun and her comic timing is amazing," Dempsey shared with PEOPLE. "We were always playful on set anyway, and then we would get serious, but this was fun just to be playful and to make each other laugh."

This is a very important cause for the stars. In fact, Dempsey showed his passion for the cause by opening up the Patrick Dempsey Center for Cancer Hope & Healing in 2008 for patients and families in need.

Dempsey is set to make his return to TV in EPIX's 10-epsidoe adaption of Joel Dicker's The Truth About the Harry Quebert Affair, while Walsh will continue her role as Olivia Baker on season two of Netflix's 13 Reasons Why.

Watch the commercial below.

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