Mike Moustakas officially rejoined the Royals on Saturday, signing a one-year contract with a mutual option for 2019.
Moustakas will be guaranteed $6.5 million and his contract includes $2.2 million in incentives.
"We're just really ecstatic," Royals general manager Dayton Moore said at a news conference.
"We simply don't go to back-to-back World Series and win a world championship without his contributions, without his ability to make plays."
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Moustakas became a free agent this offseason for the first time.