11th June 1953: Princess Mary the Princess Royal (left) with Queen Elizabeth the Queen Mother (1900 - 2002) and Prince Charles and Princess Anne on the balcony of Buckingham Palace.

11th June 1953: Princess Mary the Princess Royal (left) with Queen Elizabeth the Queen Mother (1900 - 2002) and Prince Charles and Princess Anne on the balcony of Buckingham Palace.Getty

She's the Queen's aunt and a character in the 2019 Downton Abbey movie, but who was Princess Mary?

Princess Mary was the third child and only daughter of King George V and Queen Mary, born at Sandringham in 1897 during Queen Victoria's reign. Christened, Victoria Alexandra Alice Mary, when she was born she was fifth in line to the throne, behind her brothers Prince Edward (later Edward VIII who abdicated over his marriage to Wallis Simpson in 1936) and Prince Albert (later King George VI). Her younger brother was Prince Henry (later Duke of Gloucester).

Read more: Is this is the last known footage of Queen Victoria?

5th June 1933: Queen Mary, Queen Consort to King George V, (1867 - 1953) (left), with her daughter Princess Mary, the Princess Royal beside her, and Elizabeth the Duchess of York (1900 - 2002, right) and grandaughter, Princess Elizabeth of York travelling in a carriage at a Trooping of the Colour ceremony at St. James' s Palace, London. (Photo by Keystone/Getty Images)

5th June 1933: Queen Mary, Queen Consort to King George V, (1867 - 1953) (left), with her daughter Princess Mary, the Princess Royal beside her, and Elizabeth the Duchess of York (1900 - 2002, right) and grandaughter, Princess Elizabeth of York travelling in a carriage at a Trooping of the Colour ceremony at St. James' s Palace, London. (Photo by Keystone/Getty Images)

Mary went on to marry Viscount Lascelles, sixth Earl of Harewood House at Westminster Abbey, in 1922. The Queen Mother was one of her bridesmaids and it was the first royal wedding to be featured in Vogue

1st February 1922: Viscount Lascelle, 6th Earl of Harewood and Princess Royal Mary (Victoria Alexandra Alice) Harewood (1897 - 1965), Countess of Harewood, only daughter of George V, seen here with bridesmaids on the occasion of their wedding. (Photo by Hulton Archive/Getty Images)

1st February 1922: Viscount Lascelle, 6th Earl of Harewood and Princess Royal Mary (Victoria Alexandra Alice) Harewood (1897 - 1965), Countess of Harewood, only daughter of George V, seen here with bridesmaids on the occasion of their wedding. (Photo by Hulton Archive/Getty Images)

After her wedding, Mary became Countess of Harewood, which will also feature in 2019's Downton Abbey movie. The movie features moves to the West Yorkshire mansion to marry the 6th Earl and be visited by her parents for a grand ball.

Read more: How realistic is Downton Abbey?

The 8th Earl is hopefull Harewood will benefit from the Downton effect, with people wanting to visit the historic house. All of this is happening at a time when Princess Mary's private diaries and personal effects have been handed to the National Trust. The collection includes correspondence, diaries, clothing, and personal effects.

During WWII, Princess Mary worked as a nurse and established the Princess Mary's Gift Fund which sent £100,000 worth of Christmas presents to soldiers and sailors in 1914. She became controller commandant of the Auxiliary Territorial Service during WII and toured the country to visit wartime canteens and welfare facilities.

Princess Mary died in 1965 while walking the Harewood grounds with her eldest son and grandchildren. 

1922: From left to right; Queen Mary, King George V, with their daughter Victoria Alexandra Alice Mary, the Princess Royal, and Viscount Lascelle, 6th Earl of Harewood, on their wedding day. (Photo by W. & D. Downey/Getty Images)

1922: From left to right; Queen Mary, King George V, with their daughter Victoria Alexandra Alice Mary, the Princess Royal, and Viscount Lascelle, 6th Earl of Harewood, on their wedding day. (Photo by W. & D. Downey/Getty Images)

Harewood House was recently used as a location for Victoria, and Jane Marriott, director of the Harewood House Trust, told The Telegraph: "It's a fine balancing act to make sure you create the most wonderful spaces to recreate these films but protect the assets that the public own."

Harewood House says those who arrive at the house in period costume during the week of the film's release will be permitted free entry.