After setting the Royals' single-season home run record with 38 last season, Moustakas filed for free agency. He rejected a $17.4 million qualifying offer in November.
The Royals had been grooming Cheslor Cuthbert as a replacement at third. Manager Ned Yost said he needed to find ways to get Cuthbert at least 500 plate appearances.
Moustakas, however, never received the multiyear, mega-million dollar contract he and his agent Scott Boras anticipated. The Royals signed Moustakas to a one-year, $6.5 million contract this week with a mutual option for 2019. Moustakas can make another $2.2 million in incentives this year based on plate appearances, beginning at 225.
"It's fortunate the way it happened for us the way it did," Royals general manager Dayton Moore said Saturday. "That's as simply as I can say it at this time."
Moustakas passed his physical and was in a Royals uniform again.
"It feels like I never left," he said. "It feels great to be back home. I'm excited to be back with the organization I grew up with. I got to see some familiar faces. It's always great to come into a clubhouse and everybody give you a hug. To have an opportunity to come back to Kansas City and play baseball again, it was a no-doubter, a no-brainer for me."
With less than two weeks before the March 29 opener with the Chicago White Sox, Moustakas was getting itchy to play again. He was in Newport Beach, California, and talked with Boras.
"Trying to figure out what's going on," Moustakas said.
Moustakas said the regular season approaching, spring training winding down and the urge to play this season had "a lot" to do with his signing.
"I've [sat] for quite some time this spring training," he said.
Moore was happy to close the deal.
"Our fans are ecstatic that Moose is going to be back," Moore said. "We just can't wait to get to work together again to get going on the 2018 season. Anytime you add a talent like Mike Moustakas it helps. 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."
Boras, who attended the news conference, was not so happy with the contract.
"Across the board, Moose dotted all the I's and T's of what excellence is in his performance," Boras said. "When you have a system that delays recognition of that and demand for that, you know and you have inherent notice that the flag's been raised. We've got to adjust that."
Right-handed starter Ian Kennedy, another Boras client, welcomed Moustakas back into the clubhouse.
"I know he was expecting a big, long contract," Kennedy said. "I'm excited that we get to have him back for another year. It happened to work out that we have him for another year.
"Hopefully he can do the same thing he did last year and enter the offseason where he can have a big, long contract. But selfishly, I'm happy he's back here. Moose is such a fun personality to have around. He's such a talented hitter, that he's a great presence to have in our lineup, especially from the left side."
Moustakas called it a "blessing in disguise," he missed the first part of spring training with the birth of his son, Michael Carter, last week.
A roster spot on the Royals opened up Saturday when outfielder Jorge Bonifacio was suspended 80 games after testing positive for a performance-enhancing substance.