Guido Westerwelle passed away on Friday in Cologne, the Westerwelle Foundation announced on Facebook.

Westerwelle was 54 years old. He had been battling leukemia since his diagnosis in June 2014.

"We mourn our leader Guido Westerwelle," said his foundation on its Facebook site. "He died on March 18, 2016 at the Cologne University Clinic of complications from leukemia treatment."

After multiple chemotherapy treatments and a stem-cell transplant, Westerwelle once again appeared in public to promote his book "Between Two Lives" in November of last year.

Sending her condoleneces to Westerwelle's family and husband on Friday, Germany Chancellor Angela Merkel paid tribute to the long-time politician, who fought "with heart and passion for peace and human rights."

Describing him as "one on the best speakers the German Bundestag [the lower parliament] had ever had," Merkel said it was a "sad day for Germany's liberal movement, for Germany politics."

Political career with the FDP

Guido Westerwelle served as the head of the FDP from 2001 to 2011 and from 2009 until 2013 as Germany's foreign minister under Merkel. From 2009 until his exit in 2013, he also served as Merkel's vice chancellor.

The son of two lawyers, Westerwelle was born in 1961 in the town of Bad Honnef, near the then-West German capital of Bonn. The trained lawyer and talented parliamentary debater, was a fixture in German politics for decades, initially in the opposition.

He retired in 2013 after his liberal, pro-business party, the Free Democrats (FDP), lost all of its seats in German parliament.

The late Guido Westerwelle (R) with his husband Michael Mronz (L)

First 'out' cabinet member



Westerwelle was Germany's first openly gay cabinet minister. He publicly came out in 2004 when he brought his partner, businessman Michael Mronz, to Merkel's 50th birthday party.

"I have never lived my life in the closet - I just didn't put in the shop window, I lived it normally," he said. Westerwelle and Mronz entered into a same-sex union in 2010.

The Westerwelle Foundation website showed a photo of the politician with his husband Michael Mronz. "We battled. We had the goal in sight. We are thankful for an unbelievably fantastic time together. Love remains," a statement released by the foundation said.

'Military restraint' as foreign minister

During his time as foreign minister, Westerwelle reinforced Germany's traditional reluctance to engage in military missions abroad - even while some wished to exert the country's financial influence.

In 2011, Germany decided against taking part in NATO's military campaign in Libya - a diplomatic move that set it against its traditional Western allies.

"The culture of military restraint is more timely than ever," Westerwelle said in 2012. "I am concerned about a neo-bellicism which awakens the impression that it is possible for military interventions to be faster, more effective and 'surgical,' or without civilian victims."

During his tenure, Germany participated in six-power talks with Iran, which produced an interim deal that saw Tehran freeze or curb various nuclear activities in return for a limited easing of sanctions.

'Words fail me'

Both domestic and international politicians expressed their condolences following the announcement of Westerwelle's death.

Serbia's prime minister, Aleksandar Vucic, called the late German politician "a true friend to Serbia" on Twitter:

Christian Linder, the current leader of the FDP wrote on Twitter: "Words fail me. Guido fought so hard. The grief is enormous."

Current German President Joachim Gauck also commented on Friday: "With Guido Westerwelle, our country loses a passionate, political person who tackled his different tasks - whether in his party, his office as minister, or finally in his foundation - always with the same great personal investment. As chairman of the FDP, he led his party to great successes (…) He will be remembered as a passionate democrat and European."

Others on Twitter highlighted Westerwelle's status as a role model for the LGBT community:

rs/kms (AP, AFP, dpa)