It was a rough night for Justin Bieber at Sunday's Billboard Music Awards. He was greeted by a mixture of boos and cheers after accepting an award -- and Taylor Swift reacted in disapproval when she saw him being kissed backstage by ex-girlfriend Selena Gomez.

At the Las Vegas ceremony, Bieber won the inaugural Milestone Award, presented "for musical ingenuity and innovation." When the teen pop star went onstage to accept it, he was greeted with both a standing ovation and a chorus of boos, according to multiple reports.

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After a long pause waiting for the din to settle, Bieber told the crowd, "I'm 19 years old. I think I'm doing a pretty good job. And basically, from my heart, I really just want to say it should really be about the music. It should be about the craft."

He added, "This is not a gimmick. I'm an artist and I should be taken seriously and all this other bull should not be spoken of."

Bieber later took to Twitter to offer some thoughts about what transpired: "I love music, my fans, my family, my friends . . . And I love The Lord."

Backstage, Bieber -- who also won for top male artist and top social artist -- was caught on video greeting ex-girlfriend Gomez, with whom he has had a tumultuous on-and-off relationship. As she gave Bieber a hug and a kiss on the cheek, her friend Swift, with whom she'd walked into the room, looked at the two then turned her head and stuck out her tongue in apparent disgust.