Selena Gomez and Jack Black surprise guests at children's hospital prom

Patients and staff at the Children's Hospital of Orange County were treated to a nice surprise over the weekend as Selena Gomez, Jack Black and others showed up for the annual Oncology Prom.

The hospital posted several pictures and video on social media of the transformed space, and the patients there enjoyed a night of good old-fashioned fun.

"Boarding for our 'Around the World in One Night'- themed Oncology Prom has begun. Check out how great the space looks! Our dedicated child life team has truly transformed the hospital for our patients," according to one post.

The big event, which just celebrated its 17th year, is for teens who are cancer survivors or in treatment now, according to the Los Angeles Times.

The stars came out to support the teens and hospital staff.

"And then @selenagomez shows up at your prom .... #chocprom2018 #chocprom," one post said.

Gomez also made sure to have a little fun with some of the guests.

Then Jack Black, sang to the kids and showed them some of his funky dance moves.

Finally, "Grey’s Anatomy" actress Sarah Drew also gave her support.

Kara Noskoff, an employee with CHOC, told the LA Times the event helps teens forget about their cancer treatment and recovery for a few hours.

"They’ve lost hair, gained or lost weight, are covered in surgical scars. So, they can be here, feel safe and comfortable and be with others who know what they’re going through," she said.