San Diego Union-Tribune's Kevin Acee first reported the news on Saturday.
Bleacher Report's Scott Miller reported Hosmer's deal includes an opt-out clause after the fifth year. Hosmer will earn an average of $20 million annually through the first five seasons and $13 million per year over the final three.
Hosmer played a key role in helping the Royals reach the World Series in both 2014 and 2015, with the latter trip resulting in a championship. His resume also includes the 2016 All-Star Game MVP Award, four Gold Gloves and a Silver Slugger.
The 28-year-old infielder hit .266 with 25 homers, 104 runs batted in and 80 runs while posting a .328 on-base percentage in 2016. While he's averaged 17 home runs across his first six years in the league, he topped 20 for the first time two years ago.
He backed it up with another strong year in 2017, posting a .318/.385/.498 triple-slash line with 25 long balls and 94 RBI en route to the most complete offensive year of his career.
"That's just outside perspective. I don't play this game to be in commercials for hair products. I'm playing to try to win championships," Hosmer said. "Sure you want to give yourself the best opportunity in terms of financially, but at the same time, you want to give yourself the best chance to get to the playoffs. If this group stays together, the best opportunity is right here."
Hosmer and the Royals couldn't come to terms on an extension, though. It's a major loss for the club's long-term outlook and leaves a massive void that must be filled in the immediate future.
Meanwhile, the good news for the Padres is the deal comes just as the first baseman should be heading into his peak seasons. That limits the amount of risk that typically comes with a high-priced signing and should provide them with plenty of bang for their buck, both at the plate and in the field.
It will be intriguing to see whether he becomes an even bigger power producer capable of reaching, or even surpassing, 30 homers on an annual basis as he hits his prime.
Even if that's not the case, his across-the-board production should make him a key cog in the San Diego lineup for the duration of the contract.
Hosmer should slot in at first base with Wil Myers moving back to the outfield. That duo, along with Chase Headley and Jose Pirela, should create the heart of the Friars' order.