Berlin Mayor Klaus Wowereit announced Tuesday that he will step down in December.

Wowereit, the German capital's first openly gay mayor, has served in the post for more than 13 years.

In 2001, Wowereit coined the phrase “I'm gay, and that is a good thing” in coming out during a party speech. His 2007 autobiography was titled “...und das ist auch gut so” after his famous coming out phrase.

Construction of a new city airport appears to be behind Wowereit's surprise announcement. The project is more than four years behind schedule.

“Even the latest start date of 2016 is uncertain after a cascade of reports about corruption, shoddy planning and poor construction at the airport,” The New York Times reported. “It has been anything but the showcase of an efficient, reunited 21st century Germany originally envisaged.”

At a news conference, Wowereit, 60, called the airport project “a bitter defeat.” He also declared his love for Berlin and thanked voters for giving him the opportunity “to make a career out of my biggest hobby.”