Cast members of the show have revealed that the costumes are, in many cases, actual articles of clothing from the 1910s and 1920s. They are so fragile that they cannot be laundered, and as a result, don't smell very good.
Kate Winslet and Alan Rickman were in talks to guest star together on an episode of this show as a married couple. Kate Winslet could not do it at the time because she was expecting a baby. Alan Rickman was interested, but decided against it because Kate Winslet couldn't appear with him. The two actors starred in Sense & Sensibility (1995) alongside Harriet Walter, who appears in this series as Lady Shackleton, and Imelda Staunton, Jim Carter's real life wife who appears in the Downtown Abbey (2019) movie.
According to series creator Julian Fellowes, the parts played by Hugh Bonneville, Brendan Coyle, and Dame Maggie Smith were written for the actors who play them.
The real estate that "plays" Downton Abbey, Highclere Castle, has been the home of the Herbert family since 1679. In 1922, George Edward Stanhope Molyneux Herbert 5th Earl of Carnarvon, co-discovered the Tomb of the Egyptian Pharaoh Tutankhamun. On the show, the names of Lord Robert Crowley, Earl of Grantham's beloved dogs, Pharaoh and Isis, are nods to the real castle's connection to Egyptian history. The castle was shown briefly in Il segreto di Tutankhamen (1980).
Among the royal fans of the show was H.M. Queen Elizabeth II . She spotted errors in various episodes, according to the Daily Telegraph. She noted a World War I soldier was wearing medals awarded in World War II. The Queen had also been a guest at Highclere Castle.
Alastair Bruce: the historical advisor to this show, had at least three cameos. The first is Christmas at Downton Abbey (2011). He is clearly visible among those dining at the barn lunch after the New Year's Day shoot. The second is The London Season (2013), as the presenter before the King during the coming out ceremony. The third is in the series finale, Christmas Special (2015). He is the butler who introduced Lord and Lady Grantham to Bertie Pelham's mother at Brancaster Castle.