Justin Bieber has accused the Canadian Prime Minister of upstaging him at his own concert after making a backstage meet-and-greet look like an official get together.

The pop star was criticized for wearing overalls to what looked like a properly organized meeting with Stephen Harper at the Scotiabank Place sports arena in Ontario.

The Canadian leader showed up to honor Bieber for his career success with a Diamond Jubilee medal, created to mark the 60th anniversary of Commonwealth sovereign Queen Elizabeth II's accession to the throne - and the singer now admits he had no idea the ceremony was going to be so formal.

Appearing on the Ellen DeGeneres Show on Friday, Justin Bieber said, "I was at my concert... I was doing, like, a meet and greet, meeting all my fans and stuff and he came to the venue where I was performing."

Justin Bieber reveals the Prime Minister's entourage brought flags with them to make the backstage meeting look more official - and the pop star was caught off guard.

He adds, "It wasn't fair. That was really my event... I really promise if I would have went to his environment (sic), I would have been all done up."