Guido Westerwelle, the former German foreign minister and leader of the pro-business Free Democrats, died on Friday in Cologne. He was 54.

The Berlin-based Westerwelle Foundation for International Understanding, which he co-founded, said on its Facebook page that Westerwelle died from complications from leukemia.

“We mourn our leader Guido Westerwelle,” the group wrote. “He died on 18 March 2016 at Cologne's University Hospital of complications relating to leukemia treatment.”

Westerwelle was Germany's first openly gay cabinet minister, serving four years as vice-chancellor and foreign minister in Chancellor Angela Merkel's second cabinet.

Westerwelle was one of Germany's most well-known politicians since the 1980s.

He entered a civil partnership with Michael Mronz, an event manager, in 2010, roughly six years after publicly announcing his sexuality. The men were crowned a “power couple” by German media.