Halac's daughter, Demi, announced the news on Halac's personal Facebook page on Tuesday ... saying, "He went peacefully in his sleep. He's no longer in pain."

"This really hit home to lose my father, he will forever be in my heart and many others. I love you dad. Make the skies beautiful for me."

Halac debuted as Bruiser Mastino for the Catch Wrestling Association in the early 1990s before joining the World Wrestling Federation as Mantaur, a role based on the mythical half-man/half-beast Minotaur character ... which was fitting for his 400-pound frame.

Halac -- who was open about his battle with diabetes -- continued to compete in the ring until 2019.

Fellow wrestler Paul Neu -- AKA P.N. News -- shared a touching tribute ... saying, "This is a bitter pill to swallow. RIP Michael Halac my tag partner, great friend and brother in all sense of the word except blood."

"We fought like family,, but always made up. You will be missed. God bless your soul. Until we meet again. Love you brother."