Queen Elizabeth's charming childhood letters reveal soft side of the monarch

Queen Elizabeth's childhood letters with her best friend Sonia have been revealed this week, showing a charming insight into the young royal's mind.

The letters – now classified as historical documents – were handwritten in the 1930s by young Elizabeth, with occasional misspellings and ink smudges. They're all addressed to her friend Sonia, who the Daily Mail is calling "the only friend she ever chose for herself".

One of the earliest letters revealed that Elizabeth gave Sonia her toy horse named Ben to look after, while the family moved into Buckingham Palace after her father became King.

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In the letter, the Queen invited her friend over for dinner, adding: "Please, do you think you could bring Ben with you? Could you bear it? I am sure he enjoyed staying with you."

The letters continued for the rest of both women's lives. Elizabeth and Sonia's friendship endured decades, and the pair stayed in touch right up until the latter's death in 2012.

Sonia's daughter, Victoria d'Anyers Willis, told the outlet her mother and the Queen would catch up in person as often as possible. "They got on really well and seemed to just click," she said.

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Their friendship started how most childhood relationships do: the two girls lived nearby each other, and would play hopscotch and hide-and-seek in the private park near their Central London homes.

They became thick as thieves, attending dancing and skating lessons together, frequently having dinner at each others' houses, attended Brownies and Girl Guides together.

The letters are a great insight into their relationship, with the pair sharing the highlights of their lives with each other. In one letter, the Queen told her friend about the picnics she had with her mother, and revealed details about her new pony, Pixie.

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Sonia was in attendance at the Queen's 1947 wedding to Prince Philip in Westminster Abbey.

Sonia's daughter spoke about how the Queen would often come around to visit her mum while she was a child: "The first time I was introduced to the Queen at our house in London, I was five and my brother was three.

"I can remember having the day off school, which was very exciting, and he was practising his bow and I was practising my curtsey. I remember looking out the window for her to arrive because I thought she'd be wearing a crown. She wasn't, which was disappointing."

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"Thanks to my mother's lifelong friendship with her, we were fortunate to see a more relaxed side of the Queen," she added.