Rihanna celebrated her 25th birthday in Hawaii yesterday ... with on-again boyfriend Chris Brown by her side.

The singer posted a shot of the two of them together on her Instagram account, showing her with a huge smile on her face as she sits on his lap. "Pour it up pour it up! #birthdaybehavior," she posted along with the pic.

She also posted shots from her party, showing them eating cake and celebrating together -- see those photos in the gallery above.

Earlier in the day, the couple was also seen walking along the beach hand-in-hand.

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It's pretty clear that it's "Game On" with these two, who also attended the Grammy Awards together last week. 

It wasn't all one-on-one time with her controversial ex though, as her BFF Melissa Forde also posted some shots of RiRi's birthday celebration as well -- including this one, which came with the message "Wasted."

Will you ever get used to seeing her back with Chris, considering their violent history together? Sound off below!

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