At a party at Blenheim Palace, Mary asked the Prince of Wales (later King Edward VII) to convince Hugh Grosvenor, 2nd Duke of Westminster, to marry her daughter.
The pair were married on 16 February 1901 and moved into Grosvenor House on Park Lane, a mansion that the Duke had inherited from his grandfather.
Later they lived together at Eaton Hall, Cheshire.
The Duke was one of the richest men in the world.
 Together, they had three children:
Lady Ursula Mary Olivia Grosvenor (1902–1978), whose descendants are the only descendants of the Duchess and of the Duke.

Edward George Hugh Grosvenor, Earl Grosvenor (1904–1909), who died young.

Lady Mary Constance Grosvenor (1910–2000), who never married and became a motor racing and rally driver.

The marriage was happy at first and the couple shared many interests, including yachting and motor racing.
However, her parents' expectation of personal financial gain through the marriage and her own long absence from home affected her marriage to the conservative Duke.

In 1909, the couple's only son and heir apparent to the dukedom died following an operation for appendicitis while the Duchess was away.
The Duke accused her of neglecting the child, and the Duchess did not attend the boy's funeral.
 It was rumoured that the Duchess was having a secret liaison with the Duke of Alba, whilst her husband had what he described as his own "nocturnal adventures".
Nonetheless, the couple appeared together at social events until the birth of their youngest child, Lady Mary.
In 1913, the Duke requested separation but, with the outbreak of the First World War, the couple turned their attention to war service – the Duke joined his regiment and the Duchess sponsored a military hospital in Le Touquet, housed in a local casino.

In 1918, the Duchess was created a Commander of the Order of the British Empire for her service in the war.
The couple were divorced – on the grounds of the Duke's adultery and desertion – the following year, with the decree being made absolute 19 December 1919.
The alimony settlement of £13,000 a year he made upon her was then the largest in British legal history.

After their divorce, the Duke married three more times, including to Violet Cripps, Baroness Parmoor, Loelia, Lady Lindsay, and Anne Grosvenor, Duchess of Westminster.
 The couple remained on friendly terms after 1919, hosting their daughters' debut balls together.
 Because their subsequent interactions were amicable, it has been surmised that both parties collaborated to achieve the divorce because each wanted to end the marriage and to remarry.
At a party at Blenheim Palace, Mary asked the Prince of Wales (later King Edward VII) to convince Hugh Grosvenor, 2nd Duke of Westminster, to marry her daughter. The pair were married on 16 February 1901 and moved into Grosvenor House on Park Lane, a mansion that the Duke had inherited from his grandfather. Later they lived together at Eaton Hall, Cheshire. The Duke was one of the richest men in the world.  Together, they had three children:
Lady Ursula Mary Olivia Grosvenor (1902–1978), whose descendants are the only descendants of the Duchess and of the Duke.
Edward George Hugh Grosvenor, Earl Grosvenor (1904–1909), who died young.
Lady Mary Constance Grosvenor (1910–2000), who never married and became a motor racing and rally driver.
The marriage was happy at first and the couple shared many interests, including yachting and motor racing. However, her parents' expectation of personal financial gain through the marriage and her own long absence from home affected her marriage to the conservative Duke.
In 1909, the couple's only son and heir apparent to the dukedom died following an operation for appendicitis while the Duchess was away. The Duke accused her of neglecting the child, and the Duchess did not attend the boy's funeral.  It was rumoured that the Duchess was having a secret liaison with the Duke of Alba, whilst her husband had what he described as his own "nocturnal adventures". Nonetheless, the couple appeared together at social events until the birth of their youngest child, Lady Mary. In 1913, the Duke requested separation but, with the outbreak of the First World War, the couple turned their attention to war service – the Duke joined his regiment and the Duchess sponsored a military hospital in Le Touquet, housed in a local casino.
In 1918, the Duchess was created a Commander of the Order of the British Empire for her service in the war. The couple were divorced – on the grounds of the Duke's adultery and desertion – the following year, with the decree being made absolute 19 December 1919. The alimony settlement of £13,000 a year he made upon her was then the largest in British legal history.
After their divorce, the Duke married three more times, including to Violet Cripps, Baroness Parmoor, Loelia, Lady Lindsay, and Anne Grosvenor, Duchess of Westminster.  The couple remained on friendly terms after 1919, hosting their daughters' debut balls together.  Because their subsequent interactions were amicable, it has been surmised that both parties collaborated to achieve the divorce because each wanted to end the marriage and to remarry.
Constance Lewis