Justin Bieber has allegedly been left "mortified" after Rihanna ignored him at last weekend's Billboard Music Awards. The surprising snub came as Bieber, who scooped six awards himself, presented the Only Girl In The World singer with her Top Female Artist gong, and despite the fact the two were seen talking earlier in the evening. "The pair were chatting as Justin's girlfriend Selena [Gomez] looked on scowling," a source revealed. It was then reported that their conversation got cut short as Rihanna got dragged away by a couple of friends. A source added: "The pair resumed their chat later but when Justin went to talk to her at the show's climax her security blocked his path, telling him to 'leave it'. Justin looked mortified - he thought they were buddies." Nevertheless, Rihanna was quoted as saying it was "cool" for Bieber to have presented her with the award. (British Glamour)