Justin Bieber allegedly ranted "it's my gig, I'll go out when I want" before going out late for his performance at London's The O2 on Monday.
The 'Never Say Never' star turned up on stage nearly two hours late for the event - his first of four nights at the venue as part of his 'Believe' tour - and he was reportedly "arguing" with his management backstage before eventually starting his show.
Lindsay Gilbertson, whose daughter was at the show, told The Sun newspaper: "We were told he was kicking up a real fuss. He was saying, 'It's my show, I'll go out when I want to'."
One member of staff at The O2, who did not want to be named, said: "He was arguing with members of his management, his family. It was a really uncomfortable atmosphere. His attitude was, 'I'm the star and I can do what I want'."
Another worker, Ellie Grace, added: "I hope I never have to experience so many upset children and disappointed fans again.
"I'd love to know why Bieber felt it was alright to leave 20,000 people waiting for two hours."
Insiders also alleged the 19-year-old singer was late because he was "in his dressing room playing games".
A source claimed: "His lateness was because he didn't get out of bed until late and sat in his dressing room playing games -- even though his door was being knocked. He then threw a strop as he said he wanted a shower first, despite already being late.
"Justin arrived at the O2 at 3pm to do some meet and greets, but he didn't get up until late because he'd had a heavy night at his hotel."
But yesterday, Justin took to his Twitter account to blame "technical issues" for making him late on stage on Monday.
He wrote: "Since i have been here it hasnt been easy with the press at times but I have loved it. so let me say this ... last night i was scheduled after 3 opening acts to go on stage at 935 not 830 but because of some technical issues i got on at 10:10... so i was 40 min late to stage. there is no excuse for that and I apologize for anyone we upset. However it was great show and Im proud of that. (sic)"
Despite his Monday tardiness, Justin turned up two minutes early for his gig at The O2 last night.