While celebrating his 32nd birthday in Las Vegas on Friday night, the Backstreet Boy vocalist proposed to his girlfriend Rochelle Deanna Karidis on the stage of Hard Rock Hotel's Wasted Space nightclub.

"He got up on stage and the DJ turned the music off. He asked her to come up on stage and he got down on his knee and she squatted down with him," an eyewitness tells PEOPLE. "He asked her and she said yes and hugged him. He took the ring out of his pocket and put it on her hand."

"She seemed very surprised and didn't seem to know why he was getting on stage," the witness adds. "Even his friends were shocked. They all knew he was going to propose but didn't think he would do it tonight." McLean, a source tells PEOPLE, purchased the engagement ring just a few hours before the public proposal at Hard Rock Hotel's jewelry store, Rocks.

Aside from his friends, the club was filled with patrons in Las Vegas for the AVN Adult Entertainment Expo convention. The club was hosting a party for the website "Naughty America" when McLean proposed just after midnight.