Robert F. Kennedy Jr's daughter Kick Kennedy is mourning the passing of her billionaire banker beau's death.

Kick Kennedy, the granddaughter of the late Robert F. Kennedy, had been dating banking heir Matthew Mellon, ex-husband of Jimmy Choo co-founder Tamara Mellon, for four months.

Kennedy paid tribute to her late beau on Instagram, saying, "It was hard not to be completely under his spell."

Rest In Peace, the unforgettable Matthew Taylor Mellon. Most who knew Matthew knew he had an incredible way of manifesting wildly unpredictable miracles that shocked and awed us all, over and over again. Simply, he was magical. We also couldn’t really understand what he was ever talking about, almost ever. He had a way of moving around quickly and mumbling and then all of the sudden saying something completely insightful. I remember him turning to me once and saying “Don’t let the fear of losing be greater than the excitement of winning” before going back to the usual topics (UFOs....!!! Human cloning...!!!). It was hard not to be completely under his spell and go, yes, Matthew, couldn't agree more! Matthew loved his friends. And as anyone who knew Matthew knows, it was GREAT to be his friend. He was the most generous and fabulous person I have ever met and really only cared about how everyone else was feeling. Tamara and Nicole were the loves of his life, and above all he adored his children, Minty, Force, and Olympia. They will inherit his charm, his wisdom, and a spectacularly bizarre wardrobe. Thank you MM for taking us all on the fun and captivating adventure that was your life, as you would say, in “M E L L O N S T Y L E”

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Mellon, who struggled with an Oxycontin addiction but had been sober for some time, died suddenly in Cancun, Mexico, where he was being treated at a rehabilitation center after "falling off the bandwagon".

The father-of-three (he has a daughter named Araminta with Tamara Mellon, and two children named Force and Olympia with fashion designer ex-wife Nicole Hanley) was previously reported to spend $100,000 a month on the drug.

According to the New York Post, Mellon (58) was in Cancun to try the controversial opioid-addiction treatment ibogaine which is illegal in the US. 

The previous week, a sober Mellon had enjoyed Kennedy's 30th birthday celebrations.

A spokesperson for the Los Angeles-based model said that Kennedy is "heartbroken".

“She is heartbroken, shocked, she didn’t see this coming. She is devastated and will not be making comment," Christine Schott said.

The couple had recently traveled to Switzerland, London, Washington, D.C. and New York.

“He was sober and they were enjoying life,” Schott explained. “Then all of a sudden he apparently fell off the wagon.”

She believes Mellon started using substances again sometime last week. “They were having a great time. Her 30th birthday [party] was supposed to be Friday night,” Schott said. “I understand he wanted to stay but it was decided he needed help.”

Read more: Hero or villain? Ted Kennedy's darkest hour recalled in Chappaquiddick movie

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