Petr Kellner, a billionaire art collector who is reportedly the wealthiest man in the Czech Republic, was killed in a helicopter crash in Alaska on Saturday night. He was 56.

Kellner, who is estimated to be worth $17.5 billion, is the founder of the investment group PPF.

“With great sadness, PPF announces that on March 27, 2021, majority shareholder of PPF Mr. Petr Kellner tragically passed away in a helicopter accident in the Alaskan mountains. The incident, in which five lives were lost, is under investigation,” reads a statement on the PPF website. “We want to express our gratitude for the condolences, well wishes, and prayers expressed so far to the bereaved.”

The crash happened near Knik Glacier, the ski lodge that chartered the aircraft, an Airbus AS350 B3 helicopter, according to the New York Times. A sixth person, who has not been identified, survived the crash and is in critical condition.

PPF runs exhibition spaces in Prague, including the Josef Sudek Studio and the Václav Špála Gallery, and manages extensive collections of photographs and paintings, according to the Kellner Family Foundation website. It also promotes Czech art in the country and abroad.

Kellner is survived by his wife, Renáta Kellnerová, and their four children. The foundation’s site described them as “connoisseurs and collectors of fine art.” They own, among other things, one of the largest collections of photographs by Josef Sudek, as well as work by František Drtikol, Ivan Pinkava, and Ton Stan. Kellnerová and Kellner established their family foundation in 2009.

The other victims of the crash included another guest of the Tordrillo Mountain Lodge, Benjamin Larochaix, and two of the lodge’s guides, Gregory Harms and Sean McMannany, as well as the helicopter’s pilot, Zach Russel, the New York Times reported.