Through sincere messages of condolence, the public often gets a rare glimpse into the personal relationships shared between royals.

One such letter sent to the late Queen Elizabeth II following the death of her husband, Prince Philip, revealed the close ties between the English and Spanish monarchies.

Writing to the then Queen, King Felipe of Spain opened the letter with "Dear Aunt Lilibet", indicating his close personal affections for the British Queen.

King Felipe VI, reigning King of Spain since 2014, is a third cousin once removed of the late Queen, and subsequently also a distant relative of the current monarch King Charles III.

Writing to his 'Aunt Lilibet', King Felipe expressed his sadness over the passing of his 'Dear Uncle Philip', highlighting a similar fondness for the late Duke of Edinburgh.

King Felipe's father, King Juan Carlos, is a great, great, grandchild of Queen Victoria, as was the late Queen Elizabeth.

In another profound tribute written to King Charles III following the death of his mother in 2022, King Felipe wrote: "Her Majesty Queen Elizabeth has undoubtedly witnessed, written and shaped many of the most relevant chapters in the history of our world during the last seven decades".

He described how the late monarch "set an example for all of us" and how she had left behind a "valuable legacy for future generations".

He added: "You are all in our hearts and thoughts. We will miss Her dearly."

'Lilibet' was a childhood nickname of Queen Elizabeth II, reportedly stemming from her difficulty, as a toddler, to pronounce her full name.

It is known that a few close relatives, including her sister Princess Margaret and her husband Prince Philip, affectionately continued using the nickname to refer to the Queen in later years.

In 2021, Prince Harry and Meghan Markle welcomed their second child together, a daughter named Princess Lilibet in tribute to her great-grandmother.

Lilibet is the second child born to the Duke and Duchess of Sussex after their son, Prince Archie.

In addition to her first name, Lilibet's middle name is Diana, another tribute to Prince Harry's late mother, Princess Diana.