The X Factor boyband singer is said to have been on several dinner dates with Rithiely 'Rithy' Pereira, who appeared on BBC One's So You Think You Can Dance last year.
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The Brazilian was booked as a backing dancer on The X Factor a few weeks ago, before meeting Hamblett backstage, reports The Sun.
A source said: "JJ couldn't take his eyes off Rithy the first time he spotted her backstage at The X Factor.
"They started chatting and she agreed to go out with him for a date. Now he's really into her."
Union J have reached the semi-final stage of the ITV competition after surviving the sing-off against Rylan Clark on Sunday (November 25).
The group recently stated they were proud to have improved in time, having once described themselves as the show's "weakest" singers.
The X Factor 2012 Results Show 8:
Copyright: Ken McKay/Thames/Rex Features
