Selena Gomez has met her crush ... but it's not boyfriend Justin Bieber.

Gomez, 18, posted this video to her website Monday. It shows her meeting Shia LaBeouf; Gomez had been tricked into thinking she was about to meet a fan, and when she sees it's Shia, 25, she gets adorably embarrassed!

"I'm so sorry to bother you," she tells LaBeouf. But Shia seems grateful, saying, "Thank you for being so sweet to me." After his Megan Fox PR debacle Monday, LaBeouf probably needed a little pick me up!

"He's so handsome," Gomez says moments later -- out of earshot of LaBeouf. She Tweeted a link to the video, saying, "Best..... Day..... Ever."