Mayor Ted Wheeler’s chief of staff, Michael Cox, resigned Friday.

“I hereby tender my resignation, effective Monday, January 7, 2019. Thank you for the opportunity to serve,” Cox wrote in his two-sentence resignation to Wheeler, sent via email at 10 a.m. Friday.

In a statement, Wheeler thanked Cox for his service and lauded him “not only as a trusted and loyal advisor but also as a friend.”

Wheeler’s spokeswoman, Eileen Park, declined to answer questions about whether the mayor asked for Cox’s resignation. “We will not be making further comment beyond the statement,” Park said. Cox did not respond to requests for comment.

Cox resigned several weeks after he disclosed an inter-office relationship with a subordinate on the advice of the city attorney, who counseled that disclosure was necessary to comply with the spirit of a city ethics law.

His resignation also comes halfway through Wheeler’s first term, one that has so far seen the mayor struggle to achieve his agenda. The Oregonian/OregonLive mid-term report on Wheeler’s performance concluded some of his failings occurred because his aides, led by Cox, were overworked and outmatched.

Kristin Dennis, Wheeler’s deputy chief of staff, will serve as his interim chief of staff, the mayor announced.

Cox first worked for Wheeler as his communications director when he was state treasurer. Cox then managed Wheeler’s mayoral campaign and held several roles in City Hall before being promoted to chief of staff in June.

-- Gordon R. Friedman

GFriedman@Oregonian.com; 503-221-8209