American Express president Ed Gilligan has died after falling ill on a flight to New York.
Mr Gilligan was returning home after a business trip on a corporate jet travelling with other company executives. As he was suddenly taken ill the plane was forced to make an emergency landing. He was 55.
American Express chief executive Ken Chenault wrote in a letter to employees paying tribute to the father of four.
"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. Our thoughts and prayers go out to his wife, Lisa, and their four children - Katie, Meaghan, Kevin and Shane.
"He was a proud husband and father, and his love for his family was evident in all that he did."
Chenault's letter said that more information would be available to employees next week.
Joining the company in 1980, Gilligan spent his entire 35-year career with American Express (AXP), starting as an intern and rising in the ranks to become vice president and the head of the company's business-to-business relations group in 2007.
He also headed the company's business travel unit and then the international consumer card business and was appointed president of the global bank in April 2013.
Reacting to the sad news of his sudden death, Foursquare co-founder Dennis Crowley, who worked with Amex executives on a partnership between the two companies, tweeted: "Super sad to learn about Ed Gilligan at AmEx. I got to know him thru 4SQ partnership. He was such a great person," Crowley tweeted.
Gilligan is survived by his wife and four children.