"You were everything to me .... you were a loving father, a loving man," Kseniya Mikhaleva wrote on Instagram

Kristoff St. John‘s fiancée is heartbroken following the Young & the Restless star’s shocking death.

After news of his death broke Monday, Russian-born model Kseniya Mikhaleva posted and then deleted an Instagram tribute mourning the loss of her late husband-to-be, who announced their engagement in September 2018.

“How did it happen ??? How ??? Why did you leave so early ???? and left me alone ….. I can’t believe 💔💔💔💔” she captioned a photo of St. John, who played Neil Winters on the long-running soap, kissing her forehead.

“You were everything to me …. you were a loving father, a loving man,…..how 😢😢😢😭😭😭😭💔💔💔💔 love??” she wrote. “We should doing a lot of things in future……”

She also wrote in two Instagram Stories: “So early…..so early,” with a crying face emoji and a red heart, and, “Why you are leave so early????Why…..you are always in my heart,” with a broken heart emoji.

Credit: Kseniya Mikhaleva/Instagram

To celebrate the New Year, St. John posted multiple photos of Mikhaleva to Instagram, referring to her as “my love.”

Screen Shot 2019-02-04 at 2.44.17 PM
Kristoff St. John and Kseniya Mikhaleva
| Credit: Kristoff St. John/Instagram

TMZ first reported that the actor was found dead Sunday after one of his friends went to check on him at his home in the San Fernando Valley. Police and paramedics were alerted and responded to the house, where the actor was pronounced dead on the scene. He was 52.

According to TMZ, there was no sign of foul play.

St. John’s lawyer Mark Geragos tweeted a statement, writing: “Few men had the unique strength, courage & sensitivity that @kristoffstjohn1 lived every single minute of every day. He impacted everyone he met and millions who he inspired and in turn admired him. On behalf of @MiaStJohnBoxer & @TheStJohnFamily thank you for all of your love.”

The Los Angeles Police Department confirmed to PEOPLE that a death investigation took place at around 2:05 p.m. on Sunday for a possible alcohol overdose at the 2300 block of Morea Way.

The Los Angeles County Medical Examiner-Coroner confirmed to PEOPLE that St. John was found dead at a home in Woodland Hills and was pronounced deceased at 4:02 p.m. An autopsy is scheduled for Monday.

St. John’s son Julian with ex-wife Mia St. John died by suicide in 2014 at the age of 24. Mia went on to found the El Saber es Poder (Knowledge is Power) Foundation to battle mental illness.

In 2017, St. John underwent psychiatric treatment after a reported scare regarding his mental health. According to TMZ, he threatened to kill himself with a gun and was placed under a 72-hour hold for psychiatric evaluation.

In a statement to Entertainment Tonight at the time, Mia blasted reports about the incident that led her ex to seek help.

“I want the world to know the truth about what is happening with Kristoff, because currently there is inaccurate, and fabricated information being reported by certain online outlets,” she said. “No parent should ever have to bury their child, and for those who do, it is a nightmare that haunts you forever. The death of our beloved son Julian has taken a toll on both of us. He is an actor and while he may appear whole on the outside, his heart is broken. As a society, we need to start taking mental health seriously and realize that no one is immune.”

St. John also shares daughter Paris with Mia, as well as daughter Lola with ex-wife Allana Nadal.