Diana called Queen Elizabeth II 'Aunt Lilibet' before marriage to her son Prince Charles

Princess Diana was born into an aristocratic family that had been closely allied with the British royal family for several generations, so she was no stranger to her future family members. In fact, she used to refer to her future mother-in-law Queen Elizabeth II as 'Aunt Lilibet' prior to her marriage to Prince Charles in 1981.

Lilibet is the Queen's nickname that she coined for herself as she had difficulty pronouncing Elizabeth in childhood. However, the name stuck with her, as her younger sister Princess Margaret also started calling her Lilibet and other family members followed the suit. It is said that the monarch's recently deceased husband Prince Philip was the last person who used to call her by the moniker.

The unique name was recently transferred to the younger generation, after her grandson Prince Harry and his wife Meghan Markle chose it as the first name for their second child, a daughter, who also has her grandmother's name Diana as her middle name.

"Diana's Decades," a new ITV documentary that premiered on Thursday night, shared an interesting anecdote that even Diana used to call the Queen by the name. An off-camera narrator said while discussing her childhood, "Lady Diana was born into a world of large country houses, set in rural estates. She grew up in Park House, practically next door to the Queen, who she called Aunt Lilibet."

Park House was rented by the Spencer family from the Queen herself. It is located on the royal family's infamous Christmas holiday venue Sandringham Estate, just to the west of the monarch's main residence Sandringham House. Diana, as well as her mother Frances, were born at the historical building.

The Spencer family retained the lease of Park House until 1975, when Diana's father became Earl Spencer, after which they moved to their family home Althorp, a Grade I listed stately home and estate in West Northamptonshire. Its grounds are now home to the final resting-place of the late Princess of Wales.

After her untimely death in a car crash in Paris in 1997, Diana was interred on a small island in the middle of the ornamental Round Oval lake at the estate. A Doric-style temple with her name inscribed on top has been built across from the lake, and is a tourist attraction during July and August when the house and estate are open to the public.