Sarah, Duchess of York said the Queen was “the most incredible mother-in-law and friend” to her and she would miss her “more than words can express”.

Sarah Ferguson married the Queen’s second eldest son Prince Andrew in 1986 but the couple, then titled the Duke and Duchess of York, split up in 1992 although they have remained friends.

It was a year the Queen called her “Annus Horribilis” as it also saw the break-up of the Prince and Princess of Wales’s marriage and a serious fire at Windsor Castle.

In her tribute after the Queen’s death at Balmoral Castle on Thursday afternoon, Sarah remembered the “generosity” the Queen had shown her following the end of her marriage.

“I am heartbroken by the passing of Her Majesty the Queen,” she tweeted.

“She leaves behind an extraordinary legacy: the most fantastic example of duty and service and steadfastness, and a constant steadying presence as our head of state for more than 70 years.

“She has given her whole life selflessly to the people of the UK and the Commonwealth.

“To me, she was the most incredible mother-in-law and friend. I will always be grateful to her for the generosity she showed me in remaining close to me even after my divorce.

“I will miss her more than words can express.”

Sarah and Andrew’s two daughters, Princess Beatrice and Princess Eugenie, are among the Queen’s eight grandchildren.