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Chris Brown 's Sunday night concert turned PG-13 in a hurry ... as after he brought Kayla Nicole up onstage for a song, he grinded all over her.

Travis Kelce 's ex hit the "Breezy Bowl XX" stop at SoFi Stadium, and just before the singer began crooning "Take You Down," he pulled her into a nearby chair to be his muse for the tune.

Initially, Brown danced around Kayla while he belted out the lyrics to the love song ... but toward the end, he mounted her -- and she appeared to love every second of it.

The two had a steamy romp for around half a minute -- and the crowd went crazy. At the end of the song, Brown went in for a kiss, though the lights dimmed just before anyone could see if the two locked lips. Play video content

Unclear if the scene was merely

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