ITV premiered Princess Diana's documentary "Diana's Decades," on Thursday, July 8, which showed stories about the late Princess, including her referring to her mother-in-law by nickname before her marriage to Prince Charles.

Prince Harry and Meghan Markle shared their joyous news of welcoming a baby girl on June 4, 2021. And, the couple's choice of their daughter's name sparked a discussion about an interesting royal fact that was rarely brought up to the public.

Their second child was named Lilibet Diana Mountbatten-Windsor.

Their first daughter's name was explained by the couple, which was related to the Duke's two most important women in his life, per this article.

"Lili is named after her great-grandmother, Her Majesty the Queen, whose family nickname is Lilibet. Her middle name, Diana, was chosen to honour her beloved late grandmother, the Princess of Wales."

While Diana sadly passed away, it seems like the late mother of Prince Harry and William has another connection to her granddaughter's title, in addition to her middle name paying tribute to her.

Princess Diana Calls The Queen "Aunt Lilibet"

In the new documentary, Mirror reported that the Princess of Wales would refer to her future mother-in-law, Queen Elizabeth II, by her intimate nickname.

The said moment was a few years before she got married to Prince Charles and her entry into the royal family.

"Lady Diana was born into a world of large country houses, set in rural estates," an off-camera narrator said, as they discussed Prince Charles' ex-wife and her upbringing.

"She grew up in Park House, practically next door to the Queen, who she called Aunt Lilibet," the narrator continued.

The Queen's sentimental nickname came from when she was too young to pronounce her name, resulting in calling herself "Lilibet" instead.

Catching on, her family soon adopted this name too, with her father, George VI, quoting, "Lilibet is my pride. Margaret is my joy."

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More From The 'Diana's Decades'

Also, in a clip from the Diana documentary, family friends and former neighbors of the Princess opened up about her early years, about setting a big wedding.

In the first episode, an electrician at the wedding of one of Diana's elder sisters revealed an interesting conversation with her.

Recalling the moment Diana attended her sibling's special day, the late Princess said to him, "Nothing like this for me, Ray. It's Westminster Abbey or nothing."

While her dream didn't come true, Diana married the future King of England, Prince Charles, like a fairytale on July 29, 1981.

The couple's bid day shunned the usual royal tradition of tying the knot at Westminster Abbey as the wedding was set in St Paul's Cathedral for a bigger venue.

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