The letter reads, in part:

With the heaviest of hearts, I must share some devastating news. Ed Gilligan – President of our company and friend and inspiration to many inside and outside American Express – became seriously ill on a flight home to New York this morning and has passed away.

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 adds that, for now, Gilligan’s direct reports will report to Chenault.

Gilligan joined American Express (AXP) 35 years ago as an intern, working his way up the ranks. He was named president in 2013.