Downton Abbey producers have been left red-faced after eagle-eyed fans spotted that a new promotional image featured a plastic bottle.
The ITV period drama, usually hailed for it's period accuracy, fell victim to a modern day blunder after the offending picture emerged online.
In the photos, actors Laura Carmichael and Hugh Bonneville, who play Lady Edith Crawley and Robert, Earl of Grantham, stand pose with the rogue bottle perched on top on the mantelpiece of the ornate marble fireplace behind them.
The problem is that Downton Abbey is set in the 1920s, and plastic bottles of mineral water were not introduced into the UK until the 50s.
Although none of the other promotional shots featured any gaffes, fans couldn't help poking fun at the major faux par.
"Can't wait for the Downton Where's the Bottle? Christmas book,"one said.
Since its premiere in 2010, the show, whose fans include President Obama and his wife Michelle, has won two Golden Globes, two SAG Awards, and 10 Emmy Awards.
The fifth series of Downton Abbey returns to ITV this autumn.