Jim Carter has swapped his butler's uniform for a red number with white trim.
But the 65-year-old actor who plays Carson in ITV's hit period drama isn't doing it to bring Christmas cheer to Downton Abbey fans, he has a much more serious message to share.
Carter has pulled on Santa's iconic clothing to take part in Greenpeace's new campaign. And his dishevelled St Nick is a long way from the jolly old soul we know and love.
The Downton star appears in a hard-hitting appeal titled An Urgent Message From Santa, in which he puts the world leaders on his naughty list and pleads with viewers to help him save his melting home in the Arctic before Christmas has to be cancelled forever.
"Dear children," starts Santa. "Regrettably, I bring bad tidings."
"For some time now melting ice here at the North Pole has made our operations and our day-to-day life intolerable and impossible. And there may be no alternative but to cancel Christmas.
"I have written personally to President Obama, President Putin, all world leaders," he continues. "Sadly, my letters have been met with indifference. Needless to say these individuals are now at the top of my naughty list.
"My home in the Arctic is fast disappearing and unless we all act urgently, then, I have to warn you of the possibility of an empty stocking forevermore. Please help me."
Carter himself said: "This is a very different version of Santa from the traditional, jolly, red-faced chap – this is a Santa on his last legs.
"I want to do my part to help raise the profile of the threats posed to the Arctic by oil drilling and climate change," he continued. "So I was pleased to have this opportunity to support Greenpeace and their amazing Christmas campaign."
John Sauven, executive director of Greenpeace UK, said: "Everyone loves Santa and nobody wants him to lose his home. If enough people support our campaign to protect the Arctic, then the younger generation will be able to sleep well on Christmas Eve, safe in the knowledge that Santa's home will be saved."
Watch the video for yourself: