02/20/2012 at 11:00 AM EST
While some people were not happy
about Chris Brown's performances and win at the Grammy Awards
, his ex Rihanna
seems to be in a good place with him.
, "HAPPY BIRTHDAY ROBYN!" to the singer (real name Robyn Rihanna Fenton) on Monday, her actual birthday, and Rihanna thanked him on her own Twitter account
Likely to spark even more controversy than Brown, who pled guilty
to assaulting Rihanna in 2009, appearing at the Grammys is rumors that he was at her early birthday bash
last week and is singing on a remix
of her track "Birthday Cake," called "Cake."
Rihanna is currently rehearsing in Britain and attended Stella McCartney's show
for London Fashion Week, and tweeted to fans
: "I'll be turning 24 making mu$ic!!!"
Brown meanwhile is celebrating his recent Grammy win in South Beach. He took over the deejay booth Saturday night at Cameo with friend Tyga and partygoers enjoyed a life-size cake in the shape of a Grammy.
"Chris performed three of his hottest hits, including Look at Me Now, Another Round and Strip," a source tells PEOPLE. "The fans went wild and he stayed at Cameo till 4:30 am."
With reporting by LINDA MARX