Lady Diana Farnham - who served as the Queen's lady of the bedchamber for 34 years - died at age 90 on December 29, and her death has left the Queen feeling "very sad".
A royal source told the Daily Telegraph newspaper: "Everyone loved Lady Farnham, she was always so good-humoured. She was also a very glamorous and attractive woman."
Lady Farnham rode alongside the Queen on the way to the Diamond Jubilee service in 2012, and she was considered to be a major figure in the royal household.
The insider added: "She was always very generous to new people joining the household."
Lady Farnham's death came just weeks after Ann Fortune FitzRoy, the Duchess of Grafton, - another of the Queen's ladies-in-waiting - died on December 3.
The duchess was the monarch's Mistress of the Robes from 1967 until her death, at the age of 101.
The source reflected: "It has not been a good year for the Queen - losing her husband and then the Duchess of Grafton and now Lady Farnham.
"They were dear friends who supported the Queen on official duties. Unfortunately, a sad consequence of living a long life is that you have to say goodbye to a lot of people you care about."
The Queen actually spoke about personal heartbreak during her Christmas speech.
The 95-year-old monarch - whose husband, Prince Philip, died in April, aged 99 - said in her TV message: "Of course for many, this time of year will be tinged with sadness - some mourning the loss of those dear to them and others missing friends and family members distanced for safety, when all they really want for Christmas is a simple hug or a
squeeze of the hand.
"If you are among them, you are not alone, and let me assure you of my thoughts and prayers."