Teen heartthrob Justin Bieber was reportedly stopped from talking to Rihanna at the Billboard Music Awards by her security guards. The 17-year-old was allegedly left feeling upset when he was prevented from meeting with Rhi Rhi, 23, after approaching the California King Bed singer five times at the awards ceremony, which was held at the MGM Grand Garden Arena in Las Vegas on Sunday. An insider told British newspaper the Daily Mirror: "Justin thinks Rihanna is the most beautiful woman and supremely talented. "He is in awe of her. Justin is just a red-blooded teenager, he can't help acting like a love-sick puppy dog when he's around her." The source added: "The pair were chatting as Justin's girlfriend Selena [Gomez] looked on, scowling. Then Rihanna got dragged away by a couple of her friends. "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."