While ex Britney Spears was busy performing on her Circus tour in Canada, Kevin Federline celebrated his special day with a slew of sexy soirees in the Big Apple. The dad of four, who turned 31, had a party in his honor at New York hotspot M2 with girlfriend Victoria Prince by his side on March 19. While rowdy revelers, who included model Selita Ebanks, danced to 50 Cent’s "In Da Club," Kevin sipped Grey Goose cocktails and chatted intimately with Victoria. “She sat by him the entire night,” a fellow partier tells In Touch of the inseparable pair. On his actual birthday, March 21, Kevin and Victoria joined the aspiring rapper’s dad, Mike, for more festivities at Greenhouse. “He was having a great time!” an onlooker says. The couple also partied at the New York club the previous Wednesday evening.