Rihanna has written a song about her split from Chris Brown. The 21-year-old beauty – whose on/off boyfriend Chris allegedly assaulted her on February 8 - is believed to have penned the track 'Silly Boy' to warn him their relationship is over for good. She sings: "I said I'm not coming back / You fooled me once but you can’t have that ego turning. "Just too bad for you, that when you had me / Didn't know what to do, she's over you. "Cause you had a good girl, good girl / Girl that's a keeper / You had a good girl, good girl but didn’t know how to treat her. "So silly boy get out my face / Why do you like the way regrets taste?" A demo of the song – which featured vocals from Lady Gaga - has been posted on the internet by her rapper friend Kanye West. This is not the first time Rihanna has written a song about separation and revenge. The Barbados-born beauty was working on a track about killing a cheating partner at the time of Chris' alleged attack on her. Rihanna had teamed up with rapper Akon for the track 'Emergency Room', in which she dreams about seeking revenge on an unfaithful boyfriend by hospitalising him and removing his drip. She sang: "I'm going to leave your heart broken on the floor / You're gonna be in the emergency room / I'm standing by your bed / And so tempted to pull out your IV." Last month Chris, 20, pleased not guilty to felony assault and making criminal threats in relation to his alleged attack on Rihanna. He is accused of punching, biting and choking Rihanna until she was unconscious during an altercation in his rented silver Lamborghini. Source: Tonight