PHILADELPHIA -- It is happening. Spencer Howard will make his big league debut Sunday at Citizens Bank Park.

“I have no official announcement,” Phillies manager Joe Girardi said Saturday afternoon, “but you can expect a young right-hander to start tomorrow. I'll just leave it at that. [His] initials are S.H."

Howard’s debut in Sunday’s doubleheader against the Braves will be the most highly anticipated debut by a Phillies prospect since Aaron Nola in 2015. It might even rank near Cole Hamels’ debut with the Phillies in 2006. The hype is deserved. Howard is the No. 36 prospect in baseball, according to MLB Pipeline. He has an electric fastball and three impressive offspeed pitches (curveball, slider and changeup). Folks inside and outside the organization believe he is the real deal.

They have been clamoring for his promotion for weeks.

“If Spencer Howard isn’t starting in our rotation by Game 6 in New York against the New York Yankees, there’s a problem,” Bryce Harper said on Twitch last month. “That’s all I’ll say.”

The Phillies selected Howard, 24, in the second round of the 2017 Draft. Howard’s star skyrocketed after walking on at Cal Poly-San Luis Obispo.

“That’s one of the great things about the sport of baseball,” Phillies pitching coach Bryan Price said. “Not everybody is a prodigy. Not everybody is Alex Rodriguez or Bryce Harper, or some of these guys that were really on the map at 15, 16, 17 years old. A lot of these kids go from high school to college and they blossom. I think in Spencer’s case, he had to have that skillset in there, the aptitude and the feel. So, as the arm strength built, he has enough feel for pitching to make some really significant strides in a short period of time.”

Howard could have made the Opening Day roster, but there were service-time considerations. By keeping Howard at the team’s alternate training site in Allentown, Pa., for the first five days of the season, the Phillies guaranteed an extra year of team control.

Howard now cannot become a free agent until after the 2026 season.

“He’s a very polished guy with a big arm,” Price said.

The official roster transaction -- Howard needs to be placed on the 40-man roster -- might not be announced until Sunday. Right-hander Vince Velasquez will also start Sunday. Girardi hinted that Velasquez could pitch Game 1, which would mean Howard has Game 2.

It is inconsequential, really. Howard is here.

He could stay in the rotation following his debut, bumping somebody else to the bullpen. But it is possible that he makes a spot start Sunday and moves into the bullpen. Howard has not pitched out of the bullpen in his career, but his arm would play. The Phillies also have five more doubleheaders on the schedule after Sunday, meaning they will need a sixth starter again.

“I think there’s a number of different ways that we could use him, whether it’s starting or relieving,” Girardi said.

But once Howard is up, he will stay up. His future teammates are looking forward to it.

"His stuff is electric," Phillies second baseman Scott Kingery said. "I've faced him a couple times. It didn't turn out well for me. He's got good stuff. He's someone that can help the team. I think we're all going to be excited for it. He’s got a delivery where his glove arm comes over the top, way up in the air and just pulls it down. The ball gets on you really quick. It has good ride. He’s got some nasty offspeed stuff. If the command is there his stuff is really good.”

Price said that look from Howard is “somewhat of a throwback,” in that it used to be taught years ago.

“His fastball is electric, especially against righties, it kind of jumps at you,” third baseman Jean Segura said. “His command is pretty good. He’s going to be pretty good.”

“He’s a special talent,” right-hander Tommy Hunter said. “He’s a good kid, and he’s got a lot of talent, so it’ll be fun to see him put that on display.”