"It certainly didn't feel like there were any big holes to fill, and that's no knock on the incredible work that Jennette McCurdy did at all," Alexander, 26, tells PEOPLE of his former costar, who has since quit acting. "Her performance was seamless and really phenomenal years ago. That will always stand on its own as a really phenomenal performance, how she painted a picture of Sam."
Alexander, who plays Nevel Papperman, says the revival was "always intended to be brought back as something different" from the original series, which ran for six seasons on Nickelodeon from 2007 to 2012.
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"It's leaning heavily on the original core group because iCarly is iCarly," he says. "You want to bring back the familiar faces, like the person whose name is in the title of the show, Carly, and the core friends around her. But there was an opportunity here, I think, to diversify the cast list and to bring in some new faces. That was a really terrific opportunity to take."
"I don't think we felt some major gaps, but we did feel that there was a slightly different cast composition," he continues. "And it really worked in rehearsals and it played so well in filming. You can feel that as an actor. You don't need to have the reaction of an audience to know if a scene works. If you're good at storytelling and you're good at portraying a scene for film - and I think all of us are very qualified in that regard, we could feel that this was clicking nicely."
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"I will say that old habits die hard," Alexander says of his character, Nevel. "Once a villain, to some extent, always up to some nefarious tricks. I do think people will be incredibly surprised at the storyline arc - and it's such a clever storyline."
Alexander says Nevel hasn't necessarily "renounced his old ways" since fans last saw him, but that the revival series does "edge [things] up slightly."
"I think the adjustments are really respectful to the audience," he says. "We don't want to bring people back and bait and switch them, and suddenly this is a show they don't recognize because it's over the edge in terms of raciness or so risqué."
Off-screen, Alexander is a Wall Street reporter at Business Insider. Being a full-time journalist ultimately "suited my passions better," he says.
"This job has afforded me the chance to meet such fascinating people, both in terms of titans of business, powerful people on Wall Street, founders of companies, founders of tech startups, but also I think a real privilege has been getting to know people in their most vulnerable moments, like those students from Parkland, the teachers who had become support systems for them and that has been some of the most sensitive and human stuff that I've done," he says. "It's such a privilege to be given a look inside their lives and frankly, I would not have had that chance if not for journalism."
"I'm happy," he adds. "Because I feel like I found a vocation that I just really have enjoyed and ran with."
The iCarly revival series is now streaming on Paramount+.