PHOENIX (AP) — U.S. Sen. Jon Kyl is resigning from the U.S. Senate seat he was appointed to less than four months ago following the death of Sen. John McCain, Arizona Gov. Doug Ducey announced Friday. Kyl's decision means the Republican governor will need to appoint another replacement lawmaker.

The decision by Kyl, 76, was not unexpected. He had retired from the Senate in 2012 and said when he took the appointment in September that he only committed to serving until the end of the year. His resignation is effective Dec. 31.

Ducey sidestepped selecting a longer-term replacement after McCain died on Aug. 25, saying he picked Kyl because he was "the best possible person, regardless of politics" for the job. But Kyl made it clear he only agreed to the appointment out of a sense of duty and had no plans to stay in the job for long.

The choice of the well-respected former senator to fill McCain's seat allowed the Republican governor to avoid controversy in the midst of his re-election bid, but also nearly assured that another vacancy would come soon.

Whoever Ducey taps to replace Kyl will serve until 2020, when a special election will be held to fill the final two years of McCain's six-year term. Ducey said he will pick a replacement "in the near future."

Kyl's brief resignation letter said he decided to resign at the end of 2018 so that Ducey's new appointee "can begin the new term with all other senators in January 2019 and can serve a full two (potentially four) years."

Kyl noted that when he accepted Ducey's appointment that he agreed to serve through December and then re-evaluate whether to serve longer.

"Senator Kyl didn't need to return to the Senate," Ducey said in a statement. "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."

McCain died at age 81 at his ranch near Sedona, Arizona just over a year after he announced he had glioblastoma, an aggressive brain cancer that came with a dire diagnosis.

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Riccardi reported from Denver. Associated Press writer Paul Davenport contributed to this report from Phoenix.