10:42 AM PT -- The Miami-Dade Police Department tells TMZ Sports ... Konstantin Koltsov was found dead in an apparent suicide at around 12:39 AM on Monday at the St. Regis Bal Harbour Resort.

An investigation into the death is ongoing, but cops said no foul play is currently suspected.

Ex-NHL player Konstantin Koltsov -- the boyfriend of tennis star Aryna Sabalenka -- has died.

The hockey player's former club in Russia, Salavat Yulaev, announced the heartbreaking news Tuesday ... though further details surrounding his death were not made immediately available.

"He was a strong and cheerful person," Salavat Yulaev officials said, "he was loved and respected by players, colleagues, and fans. Konstantin Evgenievich forever wrote himself into the history of our club."

"May he rest in peace."

Koltsov got his start in the NHL after the Pittsburgh Penguins selected him with the 18th overall pick in the 1999 draft. He eventually logged time on the ice for the team in the 2002-03, 2003-04 and 2005-06 seasons.

After becoming a free agent in 2006, he jetted to play professionally in Russia, signing on with Salavat Yulaev. Following his playing days, he later returned to the team as an assistant coach.

In 2021, Koltsov began dating Sabalenka -- the No. 2-ranked women's tennis player in the country -- and the couple appeared inseparable.

Throughout their years of dating, 25-year-old Sabalenka posted him on her Instagram page often ... most recently sending him birthday wishes in April with a sweet collage of pics and videos.

Sabalenka was just seen competing at Indian Wells last week ... and had been slated to play in this weekend's Miami Open.

Koltsov was just 42 years old.

RIP.

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