The Gavin & Stacey star joined hosts Ant and Dec to chat about a prank he fell for in 2016.
He appeared on the show via video chat to reflect on the fun with the programme’s hosts.
But many viewers couldn’t believe their ears after talk show host James opened his lips.
That’s because instead of hearing character Smithy’s Essex tones, James sounded completely different.
Presenter James reflected on how the Geordie duo tricked him on the set of The Late Late Show.
Since when was James Corden so posh?
He said: "The first thing I can't believe it was 2016… time has sped up!
"I remember thinking they've got me proper in a way I never thought you could.
"It's going to be wonderful to get you both back. That's what I'm thinking!"
However, viewers commenting on social media were thinking more about why he sounded so fancy.
"Watching Ant and Dec, why is James Corden talking posh all of a sudden," wondered one Twitter user.
"Since when was James Corden so posh? #SaturdayNightTakeway" echoed someone else.
A third person tweeted: "How posh is @JKCorden these days??! @antanddec #SaturdayNightTakeway."
And another person demanded: "Why the [blank] has @JKCorden gone posh all of a sudden?"
'Does he posh up for Americans?'
One person even went as far to suggest James was 'faking' his accent.
They wrote: "Why was James Corden putting on a posh voice there? He's such a phoney."
And yet another person pondered: "Why's James Corden putting on a posh accent? Does he posh up the accent for his American audience?"
Other commenters joked James had taken on the same airs and graces as character Smithy.
In the recent Christmas episode of the BBC hit comedy, Smithy changed his accent to impress new girlfriend Sonia.
"Nah James Corden on Saturday Night Takeaway sounds so posh. Sounds like on the new Gavin and Stacey when Smiffy brings his new girlfriend round," one person remarked.
And another added: "Why does @JKCorden's natural voice sound like Smithy when he was talking all posh-like to impress Sonia? #SaturdayNightTakeaway."
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