SPOILER WARNING: This article contains major spoilers for "Summer School: Chapter Nine," the latest episode of DC's Stargirl.

Jay Garrick is the Flash of Two Worlds. In "Summer School: Chapter Nine," the latest episode of DC's Stargirl, he became the first Arrowverse character to guest star on the DC Universe Original series. However, there's a catch: Jay only appeared in the past, during a sequence of flashbacks Pat had to the Justice Society of America's glory days. Once the JSA decided to kill Bruce Gordon, Eclipso's original host, Jay decided to leave the team -- leading him to become the solo hero he was when he originally appeared on The Flash.

Speaking to CBR, Stargirl guest star John Wesley Shipp described his role in "Summer School: Chapter Nine" as "a great honor." He broke down why, exactly, Jay's morals clashed with the JSA's deadly decision and what makes him an "absolute leader" in the team. He also shared his fondness for Pat "Stripesy" Dugan's character, teased whether he'd return for more Flash and Stargirl and more.

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CBR: You've been with The Flash since the show launched in 2014, but this is the first time you've brought the character into a completely new story. What was that transition like for you?

John Wesley Shipp: You know, it's a great honor. First of all, and tactically, I got a window into why they chose me from comments that I've been getting on social media. One person had said -- actually, an interviewer -- had said that they were against joining Stargirl with the CWverse. But since they chose me, I've joined the 1990s world with The CW world, that it just seemed like such a natural fit to have me be the Flash-bassador that sort of connects the world. [laughs]

At that point, when he heard it was going to be me, he was totally into it. Of course, we officially welcomed Stargirl into the CWverse and all of the possibilities that that unlocks, but no, it's a great honor. It's a great honor, and listen, anytime that people get as excited, I'm always surprised and grateful that, really, one season of a TV show in 1990 has led to all of this interest. It's more than I could have possibly imagined.

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What is it about this character and this world that continues to draw you back into it? What about Jay makes him such a beloved character?

I love Jay most because he's the character that I'm age appropriate for now. I believe chronologically, Jay is in his 90s, but was exposed to age-reversing chemicals. So he's like late 50s, early 60s. Jay harkens back -- he is the Golden Age Flash, you know? -- harkens back to a different time.

I mean, I believe he started out fighting Nazis. He chose his father's Doughboy World War I helmet to afix wings to, that he wears on his head to this day. So there are values and there's a temperature and a formality, almost, about Jay, that when he comes in, he says, "Legacy." He says legacy.

I love the way I'm used on Stargirl, because Pat has to explain -- and I just cannot mention the character of Pat without saying what a brilliant character Luke Wilson is; you can't help but fall in love with that character, this superhero mentor, who has such an exquisite degree of empathy and insecurity. It's such an interesting combination. I can't think of another character like it in superhero entertainment.

But anyway, yeah, it's a great honor to be the one to make that first crossover and to remind not only Stargirl but remind the audience -- you know, The Flash was 50 years old when I got to it in 1990. The Flash was 50 years old and had been going on for 50 years in the comics, before I ever got to it. So there's quite a legacy to explore, and having a show built around a teenage heroine is the perfect venue to explore that legacy, to throw back to, "Okay, what were the values when Jay came out of the gate fighting Nazis? What were the values that Jay holds and represents when he shows up?"

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What were you the most excited to bring to Jay on Stargirl, that perhaps you hadn't been able to before in the Arrowverse?

It allowed me to be in my own world. You know, I will always cherish -- well, come to think of it, I played Geoff Johns' version of Henry Allen. When I heard they were doing the new Flash and I heard how Geoff Johns had blown up the Allen family and Henry was suddenly wrongfully convicted of killing his wife in front of a 10-year-old Barry, I knew that's the role I wanted, because it was so different from my origin story in 1990.

Well, I was excited that Geoff would be writing him, because who knows Jay Garrick better than Geoff? Who loves and respects the character of Jay Garrick more than Geoff Johns? So when I was told what I would be doing within this really kind of dark story -- I mean, if all you tell people is it's a superhero show built around a teenager, you're leaving out so much! There's so much shadows and light; there are so many different colors. There are so many different issues and ethics and values that are packed into these episodes, and it's fun at the same time! That made me excited to come.

When I walk into that garage, I'm walking into my world, my society; I'm a founding member. Somebody said, and I love this comment -- actually, it was the After Stargirl Podcast -- Shawn, who runs that, who said, "I feel like you're more Jay Garrick on Stargirl than you have even been allowed to be so far on The Flash." I think that's why! It just felt right. It felt, "This is my world."

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In the episode, we get to see a bit of Jay interacting with the JSA for the first time. Where would you say he fits in with that team?

I think he's one of the absolute leaders. He's a founding member. He knows he holds a tremendous amount of authority and respect. Within that, I think he sees himself as a protector of the most vulnerable.

[Director] Andi Armaganian and I talked about my first entrance in the graveyard, and she helped me set the template for the relationships going forward. Coming in the way I did, carrying a sense of authority that he has in that world -- even more authority than he has in a world where Barry Allen is a faster Flash -- that he comes in and immediately puts his hand on Pat's shoulder.

When Pat gets called down for calling him Flash out of a sense of surprise of seeing him there, Jay turns to him and calls him Stripesy with a wink and a nod. In the Justice Society scene where we're debating the pivotal issue, when Pat gets called down by Wildcat for asking a question or having a vote -- when I turn to Pat and ask for his vote, and he says, "He doesn't get a vote!" and I say, "He does" -- that's about the most pushback you see Jay Garrick give.

I tried to differentiate how I related; how was the way I related to Pat different from the rather strong hand I have to take with Wildcat, as opposed to Hourman, as opposed to the lateral pass that I pitch to Starman, because I feel like it's a lateral relationship there. But I love Jay Garrick's affection for and protection of Stripesy. I mean, Stripesy is a superhero guy! That's what I told him. I said, "You're a superhero, you're a mentor, and you're so vulnerable to the point of insecurity." It is such a wonderful combination of character. You can't help but fall in love with Pat on that show.

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This season really delves into the difference between bad and evil. How would you define those terms? In terms of that scope, how would you say Jay views the threat of Eclipso?

That is such a wonderful question. I think it's such a terrific conversation to have, when we tend to see everything in terms of black and white, when we tend to make the good the enemy of the perfect, when we don't realize that all changes incremental, to have a situation in which there is no perfect answer. Someone and something will suffer as a result of whichever way they go.

Jay feels, since that's going to happen anyway, he is enough wedded to his ethics and to the idea that the Justice Society stands for... You can think of it in terms of a country: what does America stand for? What is the idea behind the Justice Society? Jay is unwilling to sacrifice that ideal, even though it means in the short term, it would save lives.

Jay's choice is short-term pain for long-term gain. The choice that the Society makes is short-term gain, or long-term pain. Who's to say who's right? I love the moment of reflection that Sylvester has after the deed is done. They're almost like, "God." They feel it. They feel what I feel immediately, as soon as Sylvester says, "Yes, this is the end of the Society, making this choice."

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What are the odds we could see more of Jay on Stargirl in the future?

Well, I would be certainly open to having that discussion. I loved working with the cast. I'm very familiar with Atlanta; my whole family's there. I love visiting Atlanta. It's a great town. So as long as Geoff Johns is hands-on, let me just take this opportunity to invite him to pick up the phone! [laughs] Let's have that conversation!

Assuming we haven't already, and I'm not saying we haven't, because I can't say one way or the other. But yeah, I would welcome the opportunity to come play in that playground again.

I'd be remiss if I didn't ask whether or not we'll see you on the Flash again sometime soon, especially after that huge Flash family reunion. I know I'd like to see the show explore that relationship between Jay and Bart.

I would too, and they've set it up. I can tell you that I will be going back in about a week and a half to shoot more Flash.

I'm not sure exactly what time it will be, but [The Flash showrunner] Eric Wallace and I have discussed having the opportunity to explore Jay Garrick as a mentor that we missed with Wally. There was an opportunity with Wally, but we missed it. I would love now to be able to fulfill that playing Jay, that relationship that they set up and that Jordan Fisher set up and the writer set up so beautifully in those last two episodes.

Stargirl airs Tuesdays at 8 p.m. ET/PT on The CW.

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