James Corden has revealed that the child actor playing his son in the upcoming Gavin & Stacey Christmas special previously appeared in the show as a baby.

In the new reunion episode, viewers will catch up with all of the main characters introduced in the first three series of Gavin & Stacey, including Smithy and Nessa’s son, Neil The Baby (now 11 years old, but obviously still referred to exclusively as “Neil The Baby”).

As a baby, Oscar Hartland played the character in the final series of Gavin & Stacey, and was invited back to reprise the role for the new Christmas special.

During an interview on Zoe Ball’s Radio 2 Breakfast Show on Monday morning, James explained: “Shall I tell you what’s really amazing? When we shot the last series of Gavin & Stacey, Nessa and Smithy had obviously had their baby, so we had, on set, two babies who would be Neil The Baby, so if one was crying, we’d switch it out for the other one.

“The actor who is playing Neil The Baby is one of those babies. And he’s absolutely fantastic.”

Ruth Jones also noted: “And the other baby, Ewan [Kennedy] came to say hello as well, so it was lovely.”

And while the cast was tight-lipped about what to expect from Neil The Baby in the episode, Rob Brydon teased: “When you see him, you’ll totally accept that he’s the child of Ruth and James. How they found a boy that looks… I mean, I don’t know what you were doing 12 years ago, but there was nobody more [suited].”

Ruth added: “Funnily enough, Alison Steadman [Pam Shipman] said that to me yesterday. She said, ‘are you sure he isn’t yours and James’ love child?’.”

Gavin & Stacey returns to our screens on Christmas Day on BBC One.