Michaels' publicist, Joanna Mignano, said in a statement Monday the couple have separated.
Michaels and Gibson have dated on and off for about 18 years. They got engaged in 2010. They have two daughters, Raine Elizabeth and Jorja Bleu.
The statement says Michaels and Gibson will "remain great friends and are committed to jointly raising" their daughters.
Michaels was the vocalist for the band Poison. He also appeared in his own VH1 reality show.
Michaels was treated in 2010 for a brain hemorrhage. Last year he underwent a procedure to close a hole in his heart.