The man who spent decades documenting the lives of members of the royal family has accused the late Queen Mother of making a racist comment.

Speaking at the Hay Festival in Wales, diarist Sir Roy Strong revealed there was a “certain streak” in him that was protective of the Queen Mother, which is why he had not recorded instances of racial prejudice through the years.

The former director of the National Portrait Gallery and Victoria and Albert Museum adds that her racially charged comments were “too awful” to immortalise in a book, The Times reports.

“I can remember the Queen Mother came to lunch at Ham House, which was a branch of the V&A, and she said ‘I will bring the liquid refreshment, and we all know what that meant.

"Suddenly in the middle of lunch, I was on the left of her I think, and the Queen was in Africa at the time, and the Queen Mother leant over to me and said ‘Beware the blackamoors’. I can’t put that down."

The diarist made a career from publishing volumes of diaries about the royal family. The first came out in 1997 and covered 1967 to 1987, and the second volume, covering 1988-203 was released in 2003.

The Queen Mother has faced other accusations of racism. William Shawcross’ authorised biography claims that she once walked into a reception with the Japanese Prince and said ‘Nip on! Nip on”. In another instance, she reportedly told Woodrow Wyatt that she “had some reservations about Jews,” and her lady-in-waiting that “the Africans just don’t know how to govern themselves…what a pity we’re not still looking after them.”