'Young and Restless' Actor Kristoff St. John's Fiancee Mourns After His Sudden Death

Kristoff St. John's fiancée is mourning his death following The Young and the Restless star's sudden passing this week.

Model Kseniya Mikhaleva took to Instagram after news broke of her fiancé's death with a message detailing her disbelief.

"How did it happen ???? How ??? Why did you leave so early ???? and left me alone ..... I can't believe," she wrote alongside a photo of St. John kissing her forehead, adding four broken heart emojis.

"[Y]ou were everything to me .... you were a loving father, a loving man,.....how...love??we should doing a lot of things in future," she continued.

She also wrote on her Instagram Story, "Why you are leave so early???? Why ... you are always in my heart."

As previously reported, paramedics were called to St. John's home in Los Angeles, California on Sunday, where he was pronounced dead at the scene. A source close to the situation told TMZ that alcohol was suspected to be involved in St. John's death, although no official cause of death nor autopsy has been completed yet.

Mikhaleva, who is working on her degree in Moscow, told Radar Online that she last spoke to St. John on Saturday, one day before his death.

"He was [a] little bit sad because I'm in Russia," she said, adding that he wanted "to be with me always."

St. John announced his and Mikhaleva's engagement in September, posting a photo of her engagement ring alongside the caption, "She said yes."

Kristoff St. John's final tweet was one that he retweeted: "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."

St. John, 52, was a beloved star of The Young and the Restless, first appearing on the CBS soap opera in 1991, then going on to earn nine Daytime Emmy Award nominations and 10 NAACP Image Awards for his role.

In 2017, St. John was hospitalized to have his mental and emotional health evaluated. He thanked fans for their support following his stay in the clinic.

"To all of mi (sic) IG peeps. Thanks for throwing out a life preserver," he wrote in the November 2017 post. "Words cannot express the gratitude that I feel to have so much love that you bathe me in…anoint me with…cloak me with. I am humbled."

"Life is precious. I look forward to continuing this journey together with all of you…us. Because at the end of the day, at the magic hour, we are warmed with an all knowing presence of light and love," he continued. "My heart beats to the music of our creation. You are an integral piece of my personal spiritual puzzle, as I hope I am to yours. I love you…forever. #gratitude #friends #life #journey #love #yr #cbs."

St. John is survived by two daughters, Paris and Lola St. John, as well as Mikhaleva.