Thanks to social media ... Rihanna and Chris Brown can't keep their relationship a secret any longer.

The two former flames were seen getting ultra-close during Jay-Z's concert in Brooklyn at the Barclays Center.

While seated in the VIP section, Brown had his arm stretched around RiRi's chair. This sighting comes just one day after Brown was seen leaving Rihanna's NYC hotel.

Wondering what Brown's girlfriend Karrueche Tran thinks about all this. Well, IF she's still his girlfriend.

As for Rihanna, she left her NYC hotel for the concert yesterday looking hotter than ever ... with a peek-a-boo shirt. No wonder Chris couldn't resist!

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