The late Princess of Wales called 60 Coleherne Court in the city's Knightsbridge neighbourhood home from 1979 to 1981. It was a present from her parents when she turned 18, and she shared it with several of her friends.
"Diana was one of the world's most famous women and she used her fame and influence to raise awareness of issues such as homelessness and landmines," Anna Eavis, English Heritage's cultural director, said in a statement. "It is fitting that our blue plaque remembers her at this place where her life in the public eye first began."
In Andrew Morton's book Diana, In Her Own Words, the late Princess of Wales describes the apartment as the place where she spent her happiest years. She called it a "juvenile, innocent, uncomplicated [and] fun" time.
"I laughed my head off," she told the author.
Virginia Clarke was one of the friends with whom she lived, and attended the plaque's unveiling this week.
"Those were happy days for all of us and the flat was always full of laughter," she said at the unveiling, according to the Associated Press. "Diana went off to become so much to so many. It's wonderful that her legacy will be remembered in this way."
Virginia, who was known as Virginia Pitman when she lived with Diana, was the late People's Princess's roommate when she was dating Charles. Anne Bolton lived with them both during Diana's latter years in the apartment, according to The Sun. The future princess had three other roommates before them – Carolyn Bartholomew, Sophie Kimball and Philippa Coaker.
At the time, Diana was working as a nursery school assistant in Pimlico, and she continued to live in the home until the evening before her engagement to Charles was announced in February 1981.
The famously charitable and beloved Diana charged them all just £18 a week in rent, the publication writes, which with inflation is the equivalent of about $160 today.
This isn't the only time this year Diana has been honoured for what would have been her 60th birthday.
On July 1, Prince William and Prince Harry helped unveil a statue of their late mother in Kensington Palace's Sunken Garden. Diana's sons were joined by her siblings Charles Spencer, Lady Jane Fellowes and Lady Sarah McCorquodale as they revealed the Ian Rank-Broadley art, which is cast in the traditional "lost-wax" process with patina of bluish green over black. It features Diana with her arms around a girl and boy and was created at Castle Fine Arts Foundry in the Welsh borders town of Oswestry, England.
The Sunken Garden was also redesigned in Diana's honour by Pip Morrison. Work began on the garden in 2019, and it took 1,000 hours of planting to landscape. It now includes 300 tulips, 200 roses and 100 forget-me-nots. The latter were Diana's favourite flowers. There's now more than 4,000 flowers in the space, which also includes lavender plants, dahlias and sweet peas.
Diana would love these sweet tributes!