The Royals announced Sunday that they acquired shortstop Alcides Escobar, outfielder Lorenzo Cain and right-handed pitching prospects Jake Odorizzi and Jeremy Jeffress from the Brewers in exchange for Greinke, shortstop Yuniesky Betancourt and cash considerations.
"Zack Greinke is one of the top young pitchers in the game today," Brewers general manager Doug Melvin said in a statement. "We are very excited to add him to our new rotation.
"Zack brings great physical skills and athleticism to the team and is an outstanding competitor. This trade is a credit to our scouting and player development staff as their hard work and judgment provided us the talented prospects that Kansas City will be receiving. I also appreciate the support of ownership in making this deal."
"We were getting better with Marcum, now Greinke," Hart said in a text message to The Associated Press. "Brewers are for real!"
Brewers slugger Ryan Braun said the deal was "amazing" in a separate text message.
"Don't really know him much yet but really looking forward to getting to know him!" he said.
Royals general manager Dayton Moore said the deal made sense for Kansas City because the young players they acquired from Milwaukee fit into what is expected to be a wave of promising young players coming up through their system. Third baseman Mike Moustakas and first baseman Eric Hosmer could join the big league club this year.
"We expect to be competitive next year," Moore said. "We're still working to improve our baseball team."
Moore indicated it took some direct talks between he and Greinke before the pitcher agreed to waive the no-trade clause in his contract.
"He was very much open to it at the end of the day," Moore said.
Greinke was 10-14 with a 4.17 ERA for the Royals last season. It was a step back from his standout 2009 season, when he went 16-8 with a 2.16 ERA and won the Cy Young award.
There are two years left on the four-year, $38 million contract he signed with the Royals in January 2009. He is due $13.5 million each of the final two seasons, although the Brewers got an undisclosed amount of cash back from the Royals as part of the deal.
Greinke is 60-67 with a 3.82 ERA in six-plus seasons with the Royals. He sat out most of the 2006 season because of an anxiety disorder and considered quitting baseball.
"A big part of my heart will always pull for Zack," Moore said. "What he overcame, the success he had here, to the point it's not easy to make these types of deals. You would prefer to have him here and sign him long-term but it just wasn't something we could do."
Moore expects Greinke to thrive in the National League.
"This guy's one of the best fielding pitchers in the game," Moore said. "You can't bunt on him. He holds runners. He's a studier. I think he's going to do terrific."
Reports of a potential deal sending Greinke to Milwaukee surfaced online late Saturday.
With the deal, the Brewers have taken two big steps to bolster their starting rotation -- the team's main weak spot in back-to-back disappointing seasons. Earlier this month, Milwaukee made a trade with Toronto to obtain Marcum for highly regarded infield prospect Brett Lawrie.
It's an indication the Brewers are serious about making a playoff run in 2011 -- presumably making it far less likely that the team would trade first baseman Prince Fielder, who can become a free agent at the end of the season and has been the subject of widespread trade speculation.
Melvin also went all-in in 2008 with a trade for CC Sabathia, who led the team to the playoffs. With the acquisition of Greinke, the Brewers' starting staff is closer to par with Philadelphia and San Francisco in the National League.
This month's deals for starting pitching have cost Milwaukee promising young prospects who might have figured prominently in its future -- and could help the Royals' rebuilding effort.
Escobar was the Brewers' primary shortstop last season but struggled at the plate, batting .235 with 41 RBIs. Cain played 43 games for the Brewers last season, batting .306 with 13 RBIs.
Jeffress made 10 appearances for the Brewers last season, going 1-0 with a 2.70 ERA. He has been suspended twice under baseball's drug policy.
Odorizzi was perhaps the Brewers' top minor league pitching prospect, and agent Jason Wood said the team tried "very hard" to keep his client out of the deal.
"You know what? It's a nice compliment that the Royals thought highly enough of Jake to include him in the deal," Wood said. "It's quite flattering and Jake takes it as a compliment.
"I think the Royals have a quality player and person," Wood said. "Zack Greinke is a Cy Young winner who had a phenomenal year."