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. 

Brown tweeted, "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."

Source.:http://www.people.com/people/article/0,,20572057,00.html