Princess Mary, the only daughter of King George V and Queen Mary, married Henry Lascelles, heir to the earldom of Harewood, in 1922.
Two of her brothers would eventually become king - Edward VIII, who later abdicated, and George VI, the father of our present Queen.
Princess Mary became Countess of Harewood in 1929 when her father-in-law died and the title passed to her husband. They moved from their first family home, Goldsborough Hall near Knaresborough, to Harewood with their sons, George and Gerald.
Harewood remained Mary's home for the rest of her life - she died while walking on the estate with her eldest son in 1965.
Now it's been confirmed that the Grade I-listed stately home will appear in the new Downton Abbey feature film, due for release on September 13, and that the Countess will be a character in the movie.
Mary will be played by actress Kate Phillips, who portrayed Jane Seymour in Wolf Hall and Linda Shelby in Peaky Blinders.
The film is set in 1927 - picking off where the final series of the original ITV period drama ended four years ago - and the plot centres around a visit by King George V and Queen Mary to the fictional Downton Abbey estate in Yorkshire as guests of the Crawley family.
The storyline includes a segment in which the royal couple decide to visit their daughter at Harewood, where a lavish ball is thrown in their honour. Some of these scenes were filmed at Harewood, between Leeds and Harrogate, and the film trailer features shots of guests dancing on the house's terrace. In real life, Mary would still have been living at Goldsborough in 1927.
Downton creator Julian Fellowes has admitted that the story is based on a historical visit that King George V and his wife made in 1912 to Wentworth Woodhouse, the home of the Earl Fitzwilliam, as part of a tour of Yorkshire's industrial sites. Wentworth, near Rotherham, was also used for the filming of a ball scene in the movie. Among the local aristocracy invited to Wentworth in 1912 were the Earl and Countess of Harewood, future parents-in-law of Princess Mary, who was a 15-year-old girl at the time.
Staff at the Harewood House Trust, which runs the house as a visitor attraction, are now hoping that the eagerly-anticipated Downton Abbey film will spark more interest in the life of Princess Mary.
Her private letters, diaries and other possessions remain at Harewood as part of the Princess Mary Archive, and some of the items have been put on display in the past. They have recently been studied as part of a TV documentary series called The Queen's Lost Family, which focused on the lives of King George V's five children as adults.
A new exhibition at Harewood in September will capitalise on Mary's legacy, and items going on display to the public include her wedding dress train.
During the week of the film's release, anyone visiting Harewood in 1920s period costume will get free entry to the house and grounds - including the restored gardens that Mary herself tended.
Staff are used to the demands of film crews, as Harewood was also a major filming location for the ITV drama Victoria, about the life of Queen Victoria. During the Downton shoot, every clock in the mansion had to be stopped to prevent the chimes interfering with the microphones.
Harewood was also considered as Downton itself during location scouting for the original ITV series, which ended in 2015, but Highclere Castle in Hampshire was chosen instead and has since become a magnet for fans of the show from all over the world.
Princess Mary's grandson, David Lascelles, is the current Earl of Harewood.
Where else in Yorkshire has the new Downton Abbey movie been filmed?
Although none of the locations have been officially confirmed by producers, representatives of both Harewood and Wentworth Woodhouse have announced they they will appear in the film.
Other rumoured locations are Little Germany in Bradford, Pickering Station on the North Yorkshire Moors Railway, Hovingham Hall in Ryedale, Thirsk, Ripon, Castle Howard and Ampleforth College, the boarding school attended by Julian Fellowes.