The Royals drafted Montgomery in the first round (36th overall) out of Newhall (California) Hart High school in 2008. He eschewed a Cal State Fullerton scholarship to sign with the Royals.
He moved up through the Royals' farm system, advancing to Triple-A Omaha, before he was dealt after the 2012 season to the Tampa Bay Rays that included James Shields and Wade Davis going to Kansas City.
Instead of pitching for the Royals, he will be starting for the Chicago Cubs against them Tuesday night in the second contest of the three-game series.
"A lot of new guys there, but I still keep up with how everybody's going," Montgomery said. "It's always fun to pitch against former teammates and organizations. I know a lot of the guys in the front office are still here, that drafted me.
"It always gives you that little extra incentive to do well against them, but it doesn't change too much. I've had a couple of good starts against them in the last few years. I remember the very first time, in '15, I was just nervous.
"I was in Seattle and I was really just amped up, probably more than my debut. I remember I got bases loaded in the first, nobody out, end up getting out of it and throwing a shutout in that game, but it was just a little bit extra, you know."
Montgomery struck out 10 Royals in that June 23, 2015 complete game.
The Mariners traded Montgomery to the Cubs on July 20, 2016 in time for him to pick up a World Series ring, making five relief appearances against the Cleveland Indians in the Fall Classic.
"It's funny because it seems like forever ago," Montgomery said. "(The Cubs are) my fourth team. Obviously I was 18 when I came in, but they really took great care of us. I got to experience the first four years of pro ball in an organization that was really minor league first at the time. They were in rebuilding mode back in '08.
"They came up with a lot of good players from that class, in those years. So, just a lot of good memories of spring training and the different minor league systems, coming up in Burlington, Iowa, and playing in Omaha for a few years. Definitely some good memories within this organization."
Montgomery is 3-4 with a 3.90 ERA this season in 30 appearances (12 starts). In his last outing, he gave up one run and seven hits over 5 1/3 innings in a no-decision at San Diego.
Montgomery is 13-15 with a 3.98 ERA in 49 career starts. He is 8-8 with a 3.70 ERA in 31 starts with the Cubs. In his last 19 starts, Montgomery is 7-5 with a 3.90 ERA.
He is 2-0 with a 0.55 ERA in two starts and one relief appearance against the Royals. In his only outing at Kauffman Stadium, he picked up a victory June 23, 2015, giving up one run over 6 1/3 innings.
Left-handers are hitting .243 off Montgomery this season while right-handers are batting .282.
The Royals will counter with rookie right-hander Brad Keller (4-4, 3.39), who will be making his 12th start after beginning the season in the bullpen. He has never faced the Cubs.
Keller, who was a Rule 5 pick last December, is 3-3 with a 3.90 ERA since being inserted into the Kansas City rotation May 30.
The Royals have lost five straight to drop to 34-78, matching the Baltimore Orioles for the worst record in the majors.
The Royals will have to deal with Cubs MVP candidate Javier Baez, who is hitting .400 with six home runs and 14 RBIs in his past 10 games.
"He's just a dangerous, dangerous hitter," Royals manager Ned Yost said.
The Cubs downed the Royals 3-1 on Monday night with Baez belting a solo shot in the sixth and a run-producing double in the eighth.
It was the first time since July 19 that the Cubs won a series opener, dropping their previous four. They are 10-9 since the All-Star break.
They improved to 9-4 against American League opponents this year and are 36-17 in interleague play since 2016.