Page is already a familiar voice on the station, following her Sunday Morning With Joanna Page series earlier this year.
She says: "I absolutely love Christmas and I've been having a fantastic time doing my show on BBC Radio Wales, so when it came up that we could do a Christmas day show I knew that if there was anybody I'd want to share that with, it's Mat. I love working with him, he's so much fun."
Horne welcomed the idea of working with Joanna again, saying; "I jumped at the chance to do this show with Jo. I love working with Jo, I love Wales and I love doing radio.
"Christmas day is a special day and, particularly this year, it's been very challenging for a lot of people, so it's nice to feel like we might be bringing a little bit of joy."
Joining the pair on the Christmas day show as guests will be their Gavin & Stacey co-stars Melanie Walters (Gwen), Larry Lamb (Mick), Alison Steadman (Pam), Steffan Rhodri (Dave), Robert Wilfort (Jason) and Laura Aikman (Sonia). James Corden (Smithy) has also recorded a special message for the show.
Page says: "I'm really looking forward to chatting to some brilliant friends and guests on the show. We've got some really good quizzes, classic Christmas music and a bit of fun!"
Colin Paterson from BBC Radio Wales says: "We're excited to be reuniting Joanna and Mathew this Christmas. Having Wales' best loved couple, out of character, is a real treat. We hope their sense of fun will lift everyone's spirits."
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