The heartbreaking reason Kate Middleton was forced to change schools as a teenager.

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It’s hard to imagine the effervescent Kate Middleton struggled to fit in anywhere throughout her life.

The Duchess of Cambridge and mother-of-three is much-adored throughout the world; glamorous, charitable, and to many an inspiration.

But recent tales from her childhood reveal, long before she had a royal title, life wasn’t always easy for Kate.

Kate, like many of us, was bullied in school, to the point her parents had to pull her out and send her elsewhere.

When she was just 13 years old, Kate’s parents Michael and Carole Middleton abruptly pulled her out of the prestigious all-girls boarding school Downe House she attended at a cost of £28,875 (AU$52,000) because she was mercilessly bullied, The Sun reports.

Kate Middleton talks about parenting. Post continues after video.

Speaking to the paper, classmate Jessica Hay said Kate was so traumatised by the relentless teasing, she had been left an “emotional wreck” and developed eczema due to stress.

Kate’s parents then enrolled her at Marlborough College in Wiltshire, where ex-classmate Gemma Williamson, told the Daily Mail  Kate “had very little confidence” after years of bullying.

“Apparently she had been bullied very badly and she certainly looked thin and pale,” Ms Williamson told the publication.

A tutor from her time at Marlborough, Joan Gall, added that when a teenage Kate first arrived to the school, she was barely recognisable from her confident adult self.

“When she arrived she was very quiet. Coming into a big school like Marlborough was difficult, but she settled in quickly,” Ms Gall said.

“It was like a big, happy family. We would do things like bake cakes and watch videos,” Ms Gall said of the school.

Sources has attributed Kate’s bullying to her family’s social status – claiming because they were considered “new money”, she was preyed upon by her established, wealthy peers.

Her former classmate Jessica Hay, who described Kate as “perfect, well-turned out and lovely” also said jealousy made her a target of bullies.

A teacher at the first school, Ann Patching, told the Mail: “She didn’t make a big deal about (being bullied). I can’t remember if it was her or Carole who mentioned Downe House. It was a concern, but they were determined to move on.”

Kate flourished at her new school, going on to become a prefect and head of house. She was voted by her peers as “most likely to be loved by all”.

And when she married Prince William in April 2011, she made a poignant nod to her experience as a victim of bullying - asking guests to make a donation to the charity Beatbullying in lieu of gifts.

Since becoming the Duchess of Cambridge, Kate has supported her husband's advocacy for mental health awareness, and the two have spoken about their own battles with depression - Prince William notably in reference to his mother, Princess Diana's tragic death.

In January this year, the Duchess made a touching speech at a London school while taking part in a lesson about children’s mental health and wellbeing.

“We know that mental health is an issue for us all — children and parents, young and old, men and women — of all backgrounds and of all circumstances.

“What we have seen first-hand is that the simple act of having a conversation about mental health — that initial breaking of the silence — can make a real difference.

“But, as you here today know: starting a conversation is just that — it’s a start.”

According to the British press, the Duke and Duchess are considering sending their eldest son George to Marlborough, the school which helped her heal from her years of torment, over the recent royal tradition of Eton College.