Sharing a picture of his gold ring - from Welsh jewellery brand Clogau - the 42-year-old presenter gushed: "It's been a big day."
Friends and fans flooded the post with congratulatory messages, with Vernon Kay writing: "Hang on... Stag Do… Eerrrr hellllloooooo!!!!!" Welsh rugby player James Hook commented: "Congrats mate." TV presenter Riyadh Khalaf added: "AMAZING!! Congrats buddy."
WATCH: 9 of the most stunning celebrity weddings
However, it soon turned out that Gethin was not actually married, but was filming an advert for the jewellery brand in which he plays a happily married family man.
Sharing a video explaining the reason for his new 'wife', Gethin said: "Just finished filming for the day and put my phone on to lots of messages. Oops.
"It has been a big day because today I've got a wife, I've got a daughter, a son – I've got a dog! And today we celebrated Christmas and I can confirm after time travelling that the festive period is going to be brilliant.
"Yeah, I've been filming a Christmas advert for Clogau, hence the post earlier.
Gethin Jones shared this snap of his wedding band
Captioning the post, he confirmed he is still "single". He wrote: "Great day on set with @clogaugold ... these guys treat me well, a wedding and a family (inc a dog) all in one day.
"Spoiler: I didn’t *actually* get married in secret and yes, I’m still single!"
Gethin was previously engaged to Welsh singer Katherine Jenkins. However, the former couple split in December 2011 after getting together in 2007. She is now married to American painter Andrew Levitas.
The presenter has kept his personal life private
In 2014, the classical singer revealed it was the TV presenter who called off their engagement. Speaking candidly in the BBC's documentary Being Katherine Jenkins, Katherine shared: "At the end of 2011, when Gethin and I broke up, the reality of it was that, about two weeks later, I had to go on a UK tour where every night I'm singing songs of heartbreak."
The pair had been engaged for ten months and had reportedly bought a house together. She added: "Every day just trying to find the energy to cope - let alone going on stage and understand his reason for doing it.
"Meanwhile, everybody else is under the impression it was my decision, my ambition – I wanted to take over the world. It was so far from the truth." After their split, Gethin went on to date Lucy Mecklenburgh and model Katja Zwara.
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