Justin Bieber was serenaded by basketball legend Shaquille O'Neal at one of the singer's concerts in Phoenix on Tuesday.

Shaq has claimed to be a huge (literally) fan of the 'Baby' singer, so he sang to the 16-year-old: "Justin Bieber/Yes i love you/I hope you like me/I'm your biggest fan."

The basketball star, who has asked Bieber to appear on his reality show 'Shaq vs.', tweeted after the show: "I was at a justin bieber concert he had dat mug jumpin 50 thousand people dat kids a star, and I got his autograph thanks Justin."

We're not sure what Shaq sounded like - but at least we know what Bieber sounds like and what he looks like on stage...

Check it out...