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Rob Gronkowski, Camille Kostek Take Stage At Kygo Concert!!! ... Belt 'Stargazing'

EDM fans in Boston got a special surprise at Kygo's concert on Tuesday ... when local legends Rob Gronkowski and Camille Kostek took the stage to belt out a song in front of thousands of fans!!

The Norwegian hitmaker welcomed the longtime couple up on the platform at the TD Garden ... and when it was time for his big track, "Stargazing" feat. Justin Jesso -- he had them put their pipes to the test.

Gronk and Camille rehearsed for the moment backstage ... and given the former Patriots cheerleader's assessment of her boo's music abilities, she wasn't expecting him to give a Grammy-worthy performance.

"Rob is tone deaf," Camille admitted before the show.

So ... how'd they do?? Well, let's just say Gronk is one of the greatest tight ends in NFL history and an even better guy off the field. Camille, on the other hand, killed it!!

TMZ Studios

After they crooned the chorus, the two remained onstage and showed off their dance moves ... and allowed the O.G. singer Justin Jesso to take the reins.

After the song, Gronk and Camille dapped up and hugged the man of the hour ... and it certainly looked like a fun time was had by all.

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