The picture, which depicts Lord Robert Crawley (Hugh Bonneville) and daughter Edith (Laura Carmichael) standing in one of their impressive stately rooms, features an unexpected decoation on the mantelpiece; a very modern plastic water bottle. Nestled between two ornate vases, the otherwise innocuous object sticks out like a sore thumb.

Downtown Abbey
Spot the water bottle! Picture: @downtonabbey/PA

'Downton Abbey' is known for its meticulous attention to detail, and they even employ an expert, Alastair Bruce, to make sure the show is historically accurate. However it's not actually the first anachronism in the show, with previous episodes featuring television aerials, double-yellow lines and even a modern conservatory. As such, this gaffe didn't go unnoticed by leagions of eagle-eyed fans online when the picture was uploaded onto social media. 

The new series of the hit historical drama is due to hit screens this autumn, though no exact air date has been confirmed yet. The series will take place in 1924, six months after the end of the last series, and the tiny actors who play the youngest members of the cast, Sybil Branson and George Crawley, have been recast in line with the time jump. The election of the first Labour government will play a key role in the new series, dividing the Crowley house and its residents both upstairs and downstairs. 

Fans are eargerly awaiting the return of popular characters including Mary Crawley (Michelle Dockery) who was last seen still mourning the death of her husband Matthew. In addition, an exciting storyline for one of the show's most beloved characters, Lady Violet Crawley, played to perfection by Dame Maggie Smith, is also promised. 

New faces will also pop up at Downton, including Richard E. Grant as a historian and Anna Chancellor as Lady Anstruther, referred to as a “troublemaker” by Michelle Dockery

More: Everything We Know So Far About ‘Downton Abbey’ Season 5

More: Richard E. Grant is a Historian on Downton, and Has His Own Perfume