During the most recent episode of the soap opera series, Dr. Nate Hastings (played by Sean Dominic) revealed to Lili Winters (played by Christel Khalil) what he believed to be the cause of death for Neil.
"From everything I've seen and heard, it sounds like a massive stroke," he said. "It's possible he had high blood pressure and never even knew. That's why they call it the silent killer."
Prior to the cause of death reveal, Neil's body was discovered by his son Devon Hamilton (portrayed by Bryton James), who signified the death by coming downstairs in tears.
In real life, the Los Angeles County Medical Examiner cited St. John's passing as being an accidental death due to hypertrophic heart disease by way of excessive alcohol use. Examiners referred to St. John's heart muscle having "myocardial bridging," and showings signs that indicated alcohol abuse. His death was officially ruled an accident.
Following St. John's passing, it was announced that former Young and the Restless star Shemar Moore would return to reprise his role as Malcolm Winters, the younger brother of St. John's Neil.
Moore also issued a statement on his friend's passing, saying, "I'm raised an only child, but Kristoff is truly the closest thing to a brother and a brother's love and a brother's mentorship that I've ever known."
"He didn't have to embrace me the way he did. When I came in and was trying to find my way and he saw how scared I was, he saw how nervous I was," Moore continued. "He saw my six pack and all that, but he just saw me and he embraced me like a brother. If he hadn't embraced me, I would have never got my sure footing in the beginning days."
"He was the sexiest black man on television from what my aunties and grandmothers told me before I'd ever knew that I was ever going to share the stage with him on The Young & the Restless," Moore added.
In an initial statement, Moore went lamented the loss of his former co-star, saying, "I lost my brother yesterday. I've never had a brother, but you were my brother."
"You showed me the way. You were my mentor, my inspiration. You showed me what true talent was. You showed me what humility was," he continued. "I love you. I hate this. I love you, but I'm going to celebrate all your good."
Moore's two-episode The Young and the Restless storyline airs Thursday, April 25 and Friday, 26.