Senator Jon Kyl of Arizona, who was appointed to succeed the late John McCain, will resign effective December 31, leaving Governor Doug Ducey to appoint a replacement to fill the seat, the Arizona Republic reported Friday.

Kyl tendered his resignation via a letter delivered to Ducey’s office on Thursday.

“Thank you for appointing me to the U.S. Senate to fill the vacancy created by John McCain’s death,” Kyl wrote. “It has been an honor and a privilege to again serve the people of Arizona.”

“When I accepted your appointment, I agreed to complete the work of the 115th Congress and then reevaluate continuing to serve,” he continued. “I have concluded that it would be best if I resign so that your new appointee can begin the new term with all other Senators in January 2019 and can serve a full two (potentially four) years. Therefore, I will resign from the U.S. Senate effective 11:59 p.m. EST December 31, 2018.”

The governor will appoint a successor “in the near future,” according to his office.

Kyl accepted Ducey’s appointment following McCain’s late-August death with the stipulation that he would serve at least until the end of the year. In a statement after Kyl’s resignation, Ducey praised him for returning to public service after leaving the Senate in 2013.

“Senator Kyl didn’t need to return to the Senate,” Ducey said. “His legacy as one of Arizona’s most influential and important political figures was already without question. But he did return, and I remain deeply grateful for his willingness to step up and serve again when Arizona needed him. I wish him and his family all the best.”

Majority Leader Mitch McConnell reportedly prefers that Ducey appoint outgoing representative Martha McSally, who in November lost to Democratic representative Kyrsten Sinema in the race for Arizona’s other Senate seat.