Pitbull was so devastated over the tragic news of Kobe Bryant's death, he had to cancel as the headliner for a charity event ... but the show went on. Steven Tyler held his 3rd annual private dinner and Grammys watch party in Hollywood Sunday night to benefit Janie's Fund, his mission to help girls who've suffered trauma from abuse and neglect. Pitbull was scheduled as the event's musical guest, but sources close to the singer tell TMZ ... he was too heartbroken to take the stage.