Iain De Caestecker Sees Inevitable Tragedy for FitzSimmons in Agents of S.H.I.E.L.D. Season 4

07/27/2016 12:34 pm EDT

At San Diego Comic-Con, when reporters had a chance to talk to Iain De Caestecker and his co-star Elizabeth Henstridge, the "finally" moment of FitzSimmons was on the tip of everyone's tongues. In Season 3, the pair of scientists finally admitted their feelings for each other, and even overcame some significant obstacles to their relationship moving forward (you know, normal things like one of them being stranded on a planet halfway across the galaxy and falling in love with an astronaut who eventually was killed and possessed by an ancient alien godlike-being. Normal stuff.). De Caestecker is confident that they're truly happy now... but that makes him very cautious for the future of the couple this season.

"I think with any storyline, happy moments are inevitably, usually going to be followed by tragic moments, so I just see it, somewhere down the road, something has to go wrong," the actor warned Comicbook.com during an interview at the convention. "But for now they seem to be pretty happy! They got through that big bump of being able to be honest with each other, and tell each other how they feel about each other, which was a big deal for them. I think since they started at friends and were so close before they became romantic, that's quite a good foundation for a relationship, right?"

While their starting point was good for them, it did make things awkward for the pair of actors. Despite a ridiculous guest appearance by Head of Marvel TV Jeph Loeb in the video interview above, De Caestecker did express how the scene - their first kiss - was to film. The key word? Weird.

"It was weird. I think we both liked the evolution of the two characters getting together. But it was strange for us… she's like my sister, man. It was weird," he said, crumpling up his face.

Agents of S.H.I.E.L.D. returns to ABC in a new, later timeslot this fall, one that promises some darker (and sexier) storylines, according to previous interviews and panelists.

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