To take his roster spot, the Royals recalled right-handed reliever Louis Coleman from Triple-A Omaha.
Chen began this season in the Royals' rotation, but he was sidetracked after four starts (1-2 record, 7.45 ERA) by a bulging disc in his back. His rotation spot was taken by left-hander Danny Duffy. When Chen returned to the roster, he was primarily used as a long reliever.
Although he left Kauffman Stadium without talking to reporters on Friday, he was reached later by phone and indicated he wasn't really surprised by the move.
"I haven't been pitching well and I saw that they had to make some moves -- they did that to [Aaron] Crow and everything," Chen said. "So I knew that it could be a possibility."
The Royals optioned bullpen stalwart Crow to Double-A on Wednesday to create roster room, albeit temporarily. Chen's departure is permanent.
Manager Ned Yost made the announcement before Friday night's game against Cleveland.
"It was hard, but that wasn't Bruce's role. He was a starter, he fares better as a starter, but we've got starters that are doing really well right now and there just wasn't a spot for him," Yost said. "And we needed somebody that could fill that role down there and be more accustomed to it."
Chen, who worked his way back from near oblivion and Tommy John surgery with the Royals in 2009, finished his Kansas City career with a 47-43 record and a 4.53 ERA in 156 games (113 starts).
"He's been here a long time, since I've here, and I've watched him win a bunch of ballgames," Yost said. "His presence on the field as well as off the field has been big for all of us."
Coleman arrives with a record of 2-1, seven saves and a 3.86 ERA in 28 relief appearances for Omaha. He was with Kansas City earlier this season, going 1-0 with a 7.48 ERA in 20 games.
Chen this season was 2-4 with a 7.45 ERA in 13 games. Ironically, his last victory came on July 22 in a start at the Chicago White Sox, the game that started the Royals on their current 26-9 surge that put them in first place in the American League Central.
"I'm glad I was able to help this team in any way that I could and I'm very proud of everything I did to be prepared and be ready for this team," he said. "I'm just very grateful to this organization for everything."
The organization was grateful for Chen, too, especially when he led the club in victories for three straight years, 2010, '11 and '12. He was named the Royals' Pitcher of the Year in 2011 and won the Special Achievement Award in 2010.
"I can't pinpoint any one moment, but I'm very grateful for all the memories that I have," Chen said. "I made a lot of friends, I met my wife, I brought my daughters here in the summer, bought a home.
"I got to meet all my teammates when they first started their careers and now it's great to see where they are and how far they've come -- guys like [Yordano] Ventura, [Kelvin] Herrera, Crow, [Greg] Holland, [Eric] Hosmer, Moose [Mike Moustakas]. There are really, really a lot of great memories and times."
Chen had signed no less than five times as a free agent with the Royals and came back this year for $3.25 million when the club assured him a starting role. He also had a mutual option for 2015 for $5.5 million with a $1.25 million buyout.
"For everybody, for the young pitchers, for position players, he was always there to uplift you. If you had a bad game, he'd be the first one there saying, 'Hey, you're going to get 'em tomorrow.'" Yost said. "He's the guy that everybody looked to lighten the mood in all situations. He's going to be missed. A great guy."
Chen, from Panama, has pitched for 16 seasons in the Majors and the Royals were his 10th club, but he spent more time with them than any other team.
At age 37, he wants to continue his playing career, perhaps even this season.
"I want to keep pitching and I feel like I can keep working on my pitches, throw some sides, keep working hard and see what happens the next 10 days," Chen said. "If I get picked up by a team, then that's what I'd like to do. I'd like to keep pitching and I feel like I can still pitch, and maybe help somebody."