The Queen is enjoying her summer holiday in Balmoral, but Friday 21 August would have marked a particularly bittersweet day for the monarch, as it would have been Princess Margaret's milestone 90th birthday.
WATCH: Royal family releases incredible footage from the Queen and Princess Margaret's childhood
Princess Margaret passed away aged 71 on 9 February 2002 at King Edward VII's Hospital. The royal had suffered from poor health in her later years and had at least three strokes between 1998 and 2001. Just seven weeks later after Margaret's death, the Queen Mother died aged 101.
The young Princesses shared a close bond as they were growing up and spent the Second World War living in Windsor, where it was safer for them.
Elizabeth and Margaret in Windsor in 1940
Elizabeth and Margaret were both educated at home, with the younger Princess developing a strong interest in music from an early age. Margaret took up piano lessons at the age of four and later became an accomplished pianist. The royal sisters also liked to put on plays and pantomimes alongside their staff.
The Queen's sister took on royal duties with her main interests being welfare charities, music, ballet and the arts. She was patron of a number of organisations including the Girl Guides, Birmingham Royal Ballet and the Royal College of Nursing.
Princess Margaret married Antony Armstrong-Jones in 1960
Princess Margaret's love life has been widely documented in films and books. The Princess fell in love with Group Captain Peter Townsend after the war, but he was considered an unsuitable match for the Queen's sister as he was a divorcé.
Margaret went on to marry photographer Antony Armstrong-Jones in 1960, who became the Earl of Snowdon. The couple had two children together, David Armstrong-Jones and Lady Sarah Chatto. The marriage later broke down and Margaret and Antony divorced in 1978.
The Queen and Princess Margaret in Mustique in 1977
The Princess also owned a famous royal residence Les Jolies Eaux on the Caribbean island of Mustique, where she enjoyed private holidays. While the house was sold by her son David in 1999 for around £2.1million, the royals have continued to travel to the island for their summer getaways, including the Duke and Duchess of Cambridge.
Make sure you never miss a ROYAL story! Sign up to our newsletter to get all of our celebrity, royal and lifestyle news delivered directly to your inbox.