Duchess Sophie is the 'older sister Kate never had' and part of her 'private support network'

Since becoming a senior royal the Princess of Wales has remained incredibly close to her family and we often see the Middletons at special royal occasions. However, Kate has also forged strong bonds within the Royal Family too and her friendship with her aunt-in-law the Duchess of Edinburgh hasn't gone unnoticed.

Last November the Princess made one of her first public appearances since announcing she had completed cancer treatment when she attended the Service of Remembrance. Duchess Sophie stood beside her on the Whitehall balcony and when they turned to go inside, she gently placed her hand on Kate's back, comforting her.

At the time, royal author Ingrid Seward claimed to Hello! that this personal gesture was "something you wouldn't have seen a few years ago". She believes the royals are showing more warmth in public nowadays and thinks Sophie is like a sister to Kate.

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"They have a sisterly bond and Sophie is like the older sister Kate never had," Ingrid claimed.

The Duchess of Edinburgh is 17 years older than the future Queen, but the author of My Mother & I: The Inside Story of the King and Our Late Queen thinks that they'll have become even closer given what Kate has gone through in recent years.

She explained, "They are both incredibly kind girls and have a caring side to them. They are both protective of their children. Sophie has had a young family, so she knows what it's like trying to protect them while being in the royal world."

When the Princess of Wales made her diagnosis public she revealed that it had taken time to explain things to Prince George, Charlotte and Louis "in a way that is appropriate for them" and "reassure them". She asked for "space and privacy" and Ingrid has suggested that Sophie was likely part of her "private support network".

"Sophie also has experience of life-threatening illness - she nearly died when her daughter Louise was born. She has been there in the background, as part of a private support network," she said.

Although Sophie and Kate's bond might have become even stronger, the two women are understood to have been close from the start. Joining the royal family as a commoner - especially if you're marrying someone high up in the royal line of succession - can't have been easy for Kate.

Thankfully for the Princess of Wales, this was a path the Duchess of Edinburgh had already trodden and Ingrid Seward claimed that Sophie looked out for her niece-in-law.

"They have a huge amount in common having probably formed a bond very much at the beginning," she alleged. "Sophie was there for Kate in an unofficial capacity because she had the same experience of being a commoner marrying into the family. They both had really long romances with their husbands-to-be and Sophie lived at the Palace."

Because of this, they had "more knowledge than the royal brides before them" about "what they were getting into", Ingrid added.

Over the years we've seen the Princess of Wales and Duchess Sophie smiling and laughing together at different occasions - including the memorable moment Sophie almost tumbled right on to Kate in a horse-drawn carriage at Royal Ascot. Even though their roles aren't the same, they can be there for each other, empathising with what the other is going through and enjoying a warm "sisterly" relationship.