" Shark Tank" superfan Selena Gomez recently got to live her dream when her BFFs arranged for her to visit the set of the ABC reality show as a surprise birthday gift.

Turns out, she did more than just watch the taping: She quietly played a role in one Shark's decisions.

"OK, I'm gonna tell you little secret," investor Mark Cuban told ABC News. "So, there's not really an audience per se in 'Shark Tank' but I sit on the last seat on the right, where we let our guests sit."

"Well, that's where Selena was sitting," he continued. "And I said, 'OK, Selena, if you like a deal, you give me the thumbs-up. If you don't like a deal, you give me the thumbs down. And if you like it, I will go do it.'"

He wouldn't spill which ideas she voted on but said it was "super fun."

Cuban and fellow investor Robert Herjavec both agree Gomez would make a great Guest Shark on a future season. They both marveled at the fact that she stayed on set the whole day.

"We get a lot of guest Sharks -- they show up for a half hour or an hour and then they leave," Herjavec said. "She came on, lots of excitement ... three hours later, she's still there."

Cuban added, "Her friends, their eyes are rolling over, but Selena's, like, leaning forward and all excited ... so it was a lot of fun."

"Shark Tank" debuted its 11th season on Sunday.