"HAPPY BIRTHDAY ROBYN!," Brown tweeted to Rihanna ... would be making an appearance on Rihanna's soon-to-be released "Cake" remix. In fact, it looked like they were kinda encouraging it.

Brown, 22, tweeted “HAPPY BIRTHDAY ROBYN!” to the Barbadian singer whose ... and is also singing on a remix of her track Birthday Cake called Cake.

"HAPPY BIRTHDAY ROBYN!" Chris tweeted earlier today. The two artists are rumoured to have worked together recently on a remix to Rihanna's 'Talk That Talk' album track 'Birthday Cake', although no ...