The Irish star had just finished a performance when the Canadian cutie pounced - and band mate Tom Parker, 23, found it hilarious.
'Siva limped into the dressing room and asked, "Why's he picking on me?" It was funny,' says Tom.
But the 18-year-old had better watch his back, as it sounds like Siva, 23, is planning to get his revenge - perhaps when the lads meet at the Summertime Ball in London next month.
'Who'd win a fight, me or Beiber? Exactly,' Siva tells the Daily Mirror. 'You cannot go around hitting children.
'But I'll get him back.'
Watch this space...
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Beth Shearing
