Angela Kelly, who has worked for the Royal Household for the past 25 years, discloses in "The Other Side of the Coin: The Queen, the Dresser and the Wardrobe" that, as of this year, the monarch has moved away from using real fur.
Kelly writes: "If Her Majesty is due to attend an engagement in particularly cold weather, from 2019 onwards fake fur will be used to make sure she stays warm."
Claire Bass, executive director of animal charity Humane Society International/UK, said her organization was thrilled by the move, according to the UK's PA news agency.
Bass said: "Queen Elizabeth's decision to 'go faux' is the perfect reflection of the mood of the British public, the vast majority of whom detest cruel fur, and want nothing to do with it."
She added that the head of state's decision would send "a powerful message that fur is firmly out of fashion."
She also called on the UK government to lead the way by becoming the first country to ban the sale of fur.
Over the years, the royals have been chastised for using real fur.
In 2013, the Queen was urged by PETA, an animal rights charity, to get "with these more enlightened times."
Over the decades, the monarch has worn fur at many engagements and was often seen wearing a brown fur coat, which she first debuted in the 1960s.
At this stage, it is not clear whether the Queen's wardrobe change will extend to her historic robe of state, which she wears at the State Opening of Parliament.
The robe in question consists of an ermine and velvet cape.