Arizona Sen. Jon Kyl is set to leave after taking over for John McCain

As expected, late Sen. John McCain's replacement is stepping down at the end of this year.

Following the longtime senator's death in August, fellow Arizona Republican Jon Kyl was appointed to take his spot. Kyl served three Senate terms alongside McCain before retiring in 2013, and only promised to serve until the end of the year. He officially submitted his resignation letter Friday, leaving Arizona Gov. Doug Ducey (R) to appoint another senator before a 2020 special election.

Arizona's U.S. senators have had a tumultuous year, with Sen. Jeff Flake (R) opting not to run for re-election this year and making a few last-minute bipartisan stands along the way. Rep. Kyrsten Sinema (D-Ariz.) narrowly beat Rep. Martha McSally (R-Ariz.) to win Flake's seat in November.

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Still, McSally remains popular among other Republican senators, suggesting Ducey might appoint McSally to fill Kyl's shoes next year, CNN notes. Ducey's Chief of Staff Kirk Adams has also emerged as a potential appointee, as has state treasurer Eileen Klein, AZ Central says. Regardless, whoever Ducey appoints will only get to serve until 2020 before having to defend their seat in a special election.