Now, now, boys -- don't fight!

Chris Brown sustained a bloody gash on his chin, sharing the pic on Twitter, following a nasty brawl with Drake and his posse in NYC early Thursday -- and Rihanna may have been the topic at issue.

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NYPD confirmed to TMZ that Brown, 23, and Drake, 25 -- plus their respective entourages -- had a brutal fight at WIP nightclub in downtown Manhattan. Punches and bottles were thrown during the melee, in which five people sustained minor injuries.

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Website Global Grind reports that Brown initially sent over a bottle to Drake's table; Drake then confronted Brown, punched him in the face and threw a bottle at him.

In an expletive-laden tweet that accompanied the photo of the cut on his chin, Brown wrote: "How u party wit rich n**** that hate? Lol... Throwing bottles like girls? #shameonya!."

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Speculation abounds online that the R&B/hip-hop stars first exchanged words over singer Rihanna. The "We Found Love" singer has been secretly hooking up with ex-beau Brown for the past year and has been romantically linked to Drake (real name: Aubrey Drake Graham), with whom she collaborated on his song and video, "Take Care."

This article originally appeared on Usmagazine.com: Chris Brown, Drake Have Brutal Fight -- Was It Over Rihanna?