Rihanna has bought Chris Brown a custom-made Mercedes car for his birthday.The 'Stay' hitmaker spent over $1 million on the Mercedes-Benz SLR Stirling Moss - a vehicle so exclusive that only 75 have ever been made - as a gift for her boyfriend, who turns 24 on May 5. Rihanna has also given it a personalised touch by adding his initials to the interior. A source told the Daily Mirror newspaper: ''Rihanna has spent more than a million dollars on his main gift - a custom-made car. She's had his initials put on the red leather seats.'' Rihanna, 26, has also planned a big ''surprise'' for the 'Don't Wake Me Up' singer to show how much she loves him, but her ideas may be interrupted by her gig in New York on the same day as his birthday and she won't make him fly out to see her. A source said: ''It's a surprise. All I can say is she's got a few things up her sleeve. She wants Chris to know how much she loves him and wants him and honestly, she just wants to be with him and let him know she's got his back. ''Chris treated her so bomb and surprised her with his presence when she turned 25, she wants to be with him badly when he turns 24. ''She's not going to flat out ask him to be with her - not on his birthday because she feels that's his day - but in her heart she wants him with her.''