Westminster Mayor Herb Atchison unexpectedly announced his resignation during a special study session Monday evening.

Atchison made the announcement at the end of the special session and said he resigned at the advice of his physician. His resignation went into effect following the conclusion of Monday’s special session. 

“I want to thank the residents of the city for the past four plus decades of time that I’ve had with them,” Atchison said during the meeting that was live-streamed on YouTube. 

Mayor Pro Tem Anita Seitz will fulfill the remainder of Atchinson’s term, which is set to end after elections this November. She will be sworn into the position on May 10, according to a release from the City of Westminster.

Atchison was first elected to the Westminster City Council in 1997 and served two terms before leaving due to term limits. He returned to the council in 2011 and was eventually elected as mayor two years later, according to his biography. 

Westminster will hold its next elections on Nov. 2 and three candidates have announced their candidacy for mayor: Nancy McNally, Austin Watts and Seitz, according to 9News, The Denver Gazette’s news partner.