For his final appearance in the show, St. John as Winters showed support for his adopted son.
"I'm proud of you, and I'm really glad I'm here to witness this next triumph in your life," Winters continued to Devon, played by Bryton James, during the episode.
When the entertainment for the event doesn't show up, Winters saves the day by convincing Devon's sister, Ana Hamilton, played by Loren Lott, to step up and sing instead.
The episode concluded with a tribute to St. John: "In Loving Memory of Our Dear Friend," as well as an image of the late actor.
Fans and co-stars took to social media to mourn the loss of St. John.
"I am just so gutted thinking about the amazing talent that was Kristoff St. John," Holly Robinson Peete of "21 Jump Street" wrote. "Of course everyone knows him from Y&R but I've been watching our fun scenes from Hanging [With] Mr. Cooper today thinking about the hilarious times we had on set. He will be missed."
"Young and the Restless" co-star Kate Linder tweeted, "Kristoff St. John was such a kind man and a very dear friend to me and so many at Y&R. My late husband Ron and Kristoff just adored each other too. He will be missed terribly."
Shemar Moore, another "Young and the Restless" co-star, posted a touching and heartfelt video on Instagram, captioning it: "Mr KRISTOFF ST JOHN...There is no ME without YOU!!!!! You are MY BROTHER!!! I LOVE YOU!!! Sleep my dude.... REST IN PEACE...I'll finish what YOU started!!! THANK YOU for YOUR HEART and TALENT!!!!!"
"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 told People.
St. John's son Julien committed suicide four years ago at the age of 24, after struggling with mental health.
"Grieving the loss of a child is a process. It begins on the day your child passes, and ends the day the parent joins them," one person tweeted.
"Never a truer word was spoke," St. John responded. "Thanks for posting this."
That was his last Twitter post.
Shortly after the news of St. John's death became public, CBS Television Network and Sony Pictures Television, the studio that produces "Young and the Restless," released a joint statement.
"The news of Kristoff St. John's passing is heartbreaking. He was a very talented actor and an even better person," the statement read. "For those of us who were fortunate enough to work with him on 'The Young and the Restless' for the last 27 years, he was a beloved friend whose smile and infectious laugh made every day on set a joy and made audiences love him. On behalf of the Y&R cast and crew, CBS and Sony Pictures Television, we offer our heartfelt sympathy to his family and loved ones, especially his two daughters, Paris and Lola."
"The Young and the Restless" will air another special tribute to St. John during Friday's episode on CBS at 12:30 ET.