The musician died at age 74 in October from a brain bleed after falling down the stairs at his home in New Jersey but Simmons had implied that other factors could have been behind his passing in a recent interview, although he has expressed regret after being accused of insensitivity.
The 76-year-rocker posted on social media platform X: "On reflection, I was wrong for using the words I used.
"I humbly apologise. My hand to God, I didn't intend to hurt Ace or his legacy, but upon rereading my words, I see how it hurt everyone. Again, I apologise, I've always loved Ace. Always."
Simmons had claimed in an interview that Ace - a founding member of KISS who played in the Crazy Crazy Nights band until his departure in 2002 - had refused guidance from "people who cared about him" when it came to his health.
The star told the New York Post: "He refused (advice) from people that cared about him - including yours truly - to try to change his lifestyle.
"In and out of bad decisions. Falling down the stairs - I'm not a doctor - doesn't kill you. There may have been other issues, and it breaks my heart.
"The saddest thing. You reap what you sow, unfortunately."
Simmons also found attending Ace's funeral "heartbreaking" and expressed regret that the guitarist couldn't be with the I Was Made for Lovin' You rockers when they entered the Kennedy Center Honors last weekend.
He said: "It breaks my heart. Peter Criss, our founding drummer, Paul (Stanley) and myself went to the funeral, open casket.
"It was just heartbreaking.
"Saddest of all perhaps is that Ace just couldn't stay alive long enough to sit there proudly at the Kennedy Center and listen to - I can't even tell you who's going to come out ... really impressive people, just to say how much KISS meant to them.
"What can you say - sad."
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