Petr Kellner, 56, the wealthiest Czech and the founder and owner of the PPF Group within which mobile operator Telenor Serbia operates, and four more people were killed on a heli-skiing excursion on Saturday when their chopper crashed near a glacier in Alaska, New York Times reported early on Monday.

Kellner, whose net worth has been estimated at $17.5 billion by Forbes, was aboard the Airbus AS350 B3 helicopter when it went down near Knik Glacier.

The investigation into the reason for the crash is underway.

The Czech made his first fortune in the 1990s after starting an investment fund, which he used to buy a controlling stake in the country’s largest insurance company.

Kellner is survived by a wife and four children.