ET's Keltie Knight spoke with the actor and his co-stars, Erin Doherty and Helena Bonham Carter, at the 2020 Screen Actors Guild Awards on Sunday, where O'Connor said Markle could play herself "brilliantly" on the Netflix series.
"I'm sure she could [play herself]," he said. "Yeah, I've heard [she's coming back to acting]."
"I'm sure she could do that brilliantly, if anyone could. But I feel like we're certainly not going to be there when they do," he noted.
O'Connor plays a young Prince Charles on The Crown, which will recast its major roles after season four. The show's executive producer, Suzanne Mackie, recently said she doubts they'll "ever go as far as present-day" on the series -- though it seems Markle is available, following her and Prince Harry's bombshell exit as senior members of the royal family.
"I don't know [why we're so fascinated by the royal family]," Bonham Carter told ET with a laugh. "I mean, maybe it's because they're a very rare institution that seems to have been around for so long and we can never know exactly what's going on behind closed doors."
"Ultimately, they're a family. They're an ordinary family but in extraordinary circumstances. And I think it's been a very extraordinary but very clever piece of drama. But it keeps on unfolding, as we know, in real life. But anyway, we're just glad we're in a hit," she added.
"People are fascinated by these people, so it will continue to be fascinating regardless of the way things unfold. And we definitely lucked out with a great period of time with our characters. It's a really exciting show to be a part of," Doherty chimed in.
The cast of The Crown is nominated at Sunday's SAG Awards for Outstanding Performance by an Ensemble in a Drama Series, while Bonham Carter and Olivia Colman are also nominated for their roles. See more on the royal family in the video below.