Jason Derulo -- I'm Doin' It With 50 Cent's Baby Mama After All!

Jason Derulo and 50 Cent's Baby Mama Daphne Joy are totally a thing, despite her protestations to the contrary.

TMZ broke the story last month -- the two met in the UK and had been hooking up -- but Daphne strongly denied it.

She's clearly had a change of heart, posting this pic of them in a club, as well as video of them walking hand in hand grabbed by Peek.

Our Derulo sources say the two are ringing in the New Year together at Story in Miami.