Paris Hilton is "completely heartbroken" by Presley Gerber's death.

The 27-year-old model - son of supermodel Cindy Crawford and businessman Rande Gerber - passed away at a rehab facility after a long battle with addiction issues and now Paris, 45, has opened up about their friendship - calling Presley a "beautiful soul" and admitting she will miss him "more than words can say".

In a post on Instagram, she wrote: "I'm completely heartbroken. I still can't believe this is real.

"Presley, you were such a beautiful soul. So sweet, sensitive, kind and genuine. I cared about you so much, and I'm going to miss you more than words can say.

"I'll always cherish the memories' that they made over the years - the laughs, the conversations, and just being around you.

"You had such a gentle heart and there was something so special about you that anyone who was lucky enough to know you could feel."

Paris went on to add: "I hope you knew how deeply loved you were and how many people cared about you.

"My heart is with your entire family during this unimaginable time. Rest in peace, my friend. Love you forever. You will be so deeply missed."

Presley's final red carpet appearance was in January when he turned out for the Los Angeles premiere of Paris' documentary Infinite Icon: A Visual Memoir.

News of Presley's death was confirmed by a representative for Cindy, Rande and Presley's actress/model sister Kaia Gerber, who told PEOPLE: "The family is asking for privacy during this very difficult and painful time."

An autopsy has yet to be completed, according to TMZ and no more details about the tragedy have been released.

Prior to his death, Presley was candid about his struggles with mental health and substance abuse, explaining that he didn't want other people to repeat his own "mistakes".

During an appearance on the Studio 22 podcast, Presley shared: "Having struggled with mental health, depression and some other things that come along with that, I think that whether I help one person or a hundred people get out of that place that I was in at one point in my life, that's all I need to do."

Presley suggested that helping other people with similar issues had become his life goal. The model was determined to ensure that other people didn't repeat his errors.

He said: "[Mental health] is an issue. It is such a big part of my life. It's a 24/7 job, and there's so much to it. That's really what I want to do: help people, whether you're depressed, you're struggling with something that is having a negative effect on your body. I mean it could be anything, and there's no judgement.

"I've seen a lot of stuff and I've learned a lot of things. What I hope I can do is have made the mistakes for some other people, so they don't have to make the same mistakes that I made."