SURPRISE, Ariz. -- The rapid ascension of right-hander Brad Keller continues.

Keller, 23, has gone from a Rule 5 Draft pick in December 2017 to making the 25-man roster and eventually the rotation in '18 to becoming the Royals' Opening Day starter in '19.

Manager Ned Yost announced Keller as his choice on Tuesday morning, just hours before Keller was scheduled to make his third Cactus League start. That game was cancelled because of rain.

“I can’t really put it all into words,” Keller said. “Last year at this time, I was in this locker room and I wasn’t even sure I’d make the team.”

The Royals open the season against the White Sox at Kauffman Stadium on March 28.

Left-hander Danny Duffy made the last two Opening Day starts for the Royals. Duffy, though, has been slowed by shoulder tightness and just resumed a throwing program a little over a week ago.

Keller seemed the logical choice after emerging as the Royals’ best starter last season. He finished the season with a 9-6 record and a 3.08 ERA

“He deserves it, man,” Duffy said. “He’s our best pitcher.”

Keller will become the second-youngest Royals pitcher to start Opening Day at 23 years, 244 days. Royals Hall of Famer Steve Busby was the youngest in 1973 at 23 years, 189 days.

“It’s definitely a huge honor,” Keller said. “It’s what you dream of as a kid. I’m really excited to get the season started on a good note.”

Keller said he really didn’t have an idea he would get the nod.

“Honestly, no I didn’t,” he said. “Honestly, any of the starters were deserving.”

And how did Keller get the news?

“[Yost] just called me into his office, and [bullpen coach] Vance [Wilson] and [pitching coach] Cal [Eldred] were in there,” Keller said. “And he said, ‘We’re 50-50 on it. Vance says no, he wants you in the bullpen, and Cal wants you in the rotation.’ They made a joke of it, but it was awesome.”

Duffy said he would give Keller this advice on an Opening Day start, a day that can throw off a pitcher’s routine: “You just have to keep it like your normal routine, like it’s just another day. Don’t worry about all the noise, the fireworks, whatever. Just keep it normal.”