The upcoming finale sees Gavin, Stacey, Smithy, and Nessa getting back together one final time - after the 2019 Christmas special finished with Jones' character Nessa proposing to Smithy, played by Corden.
"It may sound like complete nonsense, but it doesn't really feel like we're in charge of writing it," said Corden.
"I feel like we just have to be together and we sort of open a portal and the characters arrive and they tell us what they want everybody to know."