Viewers were left shocked when the climax of the episode saw Chloe Charles, the wife of Thomas' character Donte, drop dead after suffering a head injury earlier in the day.
Talking to the Daily Star about the big twist, Thomas said: "When Cameron [Roach] first approached us about the show and the storyline of what's going to happen, I was like 'What?! The first episode?!'"
He then compared the moment to a scene in Game of Thrones seasone one that saw Ned Stark shockingly beheaded: "It's a bit like Game of Thrones when Sean Bean's character dies. It's like 'how can they do that?', but there's also that shock factor as well. I think the audience will not see it coming. The fact that she gets ran over and carries on as well and then at the end, it was hard to play, it was quite emotional."
The Waterloo Road revival also sees Thomas acting with his son and niece who play his on-screen children on the show.
Commenting on working with the young members of his family on the emotional scenes, Thomas said: "I was there with Scarlett and Teddy, it was just an emotional scene to do, they were crying, it's not something you want your kids or little niece to go through. But they know that it was all part of the gig, we loved every minute of it – it was just a storyline that nobody ever saw coming."
The BBC's revival of Waterloo Road saw the return of original cast members Thomas and Katie Griffiths as Donte and Chlo as well as Angela Griffin as Kim Campbell. New cast members include Kym Marsh, Neil Fitzmaurice and James Baxter.
Watch below: New cast on Waterloo Road's 2023 reboot.