Karrueche Tran is furious about Chris Brown's relationship with Rihanna.After the 23-year-old singer rekindled his romance with the 'Diamond' singer and spent Christmas Day (25.12.12) with her, his former girlfriend Karrueche took to her Twitter page to slam the couple. In a cryptic post, she wrote: ''wishing death upon someone is some weak s**t (sic).'' While Rihanna, 24, was spotted cuddling with Chris and whispering into his ear as they watched the Lakers basketball game at the Staples Center in Los Angeles on Christmas Day, the 'Don't Judge Me' hitmaker is believed to have called and text Karrueche to wish her a ''Merry Christmas''. A source said: ''Even though he was with Rihanna, he still called Kae and told her Merry Christmas and told her how he misses her and how he hopes she was having a good day and all that s**t. ''He was texting her throughout the day, too.'' But Chris - who is still on probation for his assault on Rihanna - is said to have warned Karrueche he would be spending Christmas with the Bajan beauty. The source added: ''Chris told Karrueche he was going to be with Rihanna for Christmas like two days before Christmas. Because he had told her already, she was just like 'F**k it, whatever.' ''