Kristoff St. John’s fiancée posts heartbreaking note after his death

Kristoff St. John's fiancee is mourning the death of the "Young and the Restless" actor.

On Monday, Kseniya Mikhaleva went on Instagram to share a photo of St. John — who passed away on Sunday at the age of 52 — kissing her on the head.

"How did it happen ??? How ??? Why did you leave so early ???? and left me alone ….. I can’t believe you were everything to me …” Mikhaleva captioned the picture, according to Page Six. “You were a loving father, a loving man,…..how love?? We should doing a lot of things in future……”

In a separate post, Mikhaleva said that the late soap opera actor is "always in [her] heart."

'YOUNG AND THE RESTLESS' ACTOR KRISTOFF ST. JOHN DEAD AT 52 

St. John and Mikhaleva announced their engagement back in August, sharing a photo of the model's sparkler on Instagram.

"💍❤️ special day 31.08.2018," Mikhaleva wrote alongside the picture. "💍💑 She said yes @ksumik," St. John also wrote at the time.

On Monday, a lawyer for St. John confirmed the actor's death, saying a statement would be forthcoming.

TMZ, who first reported the news, said police responded to a call from friends of the actor who found him dead at his San Fernando Valley home on Sunday. According to the gossip site, St. John was pronounced dead at the scene.

‘YOUNG AND THE RESTLESS' STAR KRISTOFF ST. JOHN'S DEATH AT 52 DEVASTATES SOAP OPERA COMMUNITY

The 52-year-old played Neil Winters on the famous soap opera since 1991. The role earned him multiple Daytime Emmy Award nominations as well as several NAACP Image Awards.

St. John's personal life was marked by tragedy, when his son with ex-wife and boxer Mia St. John, Julian, committed suicide in 2014 while receiving treatment at a mental health facility. The family later sued the treatment center for negligence and the suit was settled, according to TMZ.

St. John is survived by his daughter Paris Nicole, whom he shared with Mia St. John. He is also survived by another daughter, Lola, who was born in 2003 while he was married to his second wife, Allana Nadal. The couple divorced in 2007 and he became engaged to Russian model Kseniya Olegovna Mikhaleva in August 2018.

Fox News' Sasha Savitsky contributed to this report.