American Express president Ed Gilligan died while flying from Tokyo to New York this weekend, media reports said. He was 55.

Gilligan was returning home to New York  from a business trip to Japan when he became ill aboard a private plane which was also carrying other company executives, American Express spokeswoman Marina Norville said.

“This is deeply painful and frankly unimaginable for all of us who had the great fortune to work with Ed, and benefit from his insights, leadership and enthusiasm,” American Express chairman and CEO Ken Chenault said in a letter to the company’s employees.

Gilligan “was a living embodiment of our values, embracing both our heritage of service, trust and integrity, as well as our entrepreneurial spirit that has helped continually transform this company through the years”, Chenault said.

Gilligan joined Amex in 1980 as an intern and held a series of executive positions with the financial services giant.