Sheikha Shamsa Al Maktoum is being kept against her will in Dubai, her supporters claim. [Image: Mirror]

A Dubai princess who hasn't been seen in public for almost 20 years told how she wanted to run away in a letter she penned as a teen, it was reported.

Sheikha Shamsa Al Maktoum's cousin in London says the princess described her desire to escape a luxurious but stifling life behind palace walls.

Shamsa, 37, is the daughter of Dubai's billionaire ruler Sheikh Mohammed bin Rashid Al Maktoum, whose wife, Princess Haya bint Hussein, is in Britain after allegedly fleeing him.

Less than a year after writing the letter, Shamsa ran away while staying at the royal family's sprawling Surrey estate, sparking a huge search.

The hunt ended two months later when Shamsa - who claimed her freedoms were restricted - was allegedly kidnapped and taken back to Dubai.

She has not been seen in public since.

Her sister and other supporters claim she has been kept drugged and against her will in a palace in Dubai.

Her letter to her cousin, a young mum in London then known as Fatima Essabri, was dated September 16, 1999, The Times reported.

Sheikh Mohammed bin Rashid Al Maktoum and one of his wives, Princess Haya. [Image: Getty]

In it, she wrote: “I was thinking of running away. I know that won’t solve any of my problems - that’s why I considered talking to my mother again. But now I’ve realised that I’m still not fulfilled!”

She added: “Don’t worry, you’re not giving me ideas and you’re not encouraging me to do anything.

"All I’m saying is that I’ve made up my mind and there’s nothing left for me to do here."

The princess wrote that she had wanted to kill herself just two weeks before penning the letter.

It is claimed her mother, Houria, found out about her escape plans.

Shamsa’s younger sister Latifa, 33, claimed in a video last year that the siblings had been held prisoner after trying to escape years earlier.

Latifa had tried to escape on a yacht to India but was allegedly recaptured by Emirati and Indian soldiers who stormed the vessel as it approaches the coast of Goa.

Essabri, 48 and now living as a man named Marcus, spoke out after being contacted by the group Detained in Dubai, which has campaigned for the release of Shamsa and Latifa.

Essabri, who is Shamsa's cousin on her mother’s side, said the then-teenage princess was angry and disappointed after her father - now aged 70 and one of the world's richest men - told her she would not be allowed to attend university.

Essabri told how he lived with Shamsa and her siblings in a Dubai palace when he was aged between 12 and 14.

They would play in Rolls-Royces parked outside the palace and go on holidays to the desert, and sometimes Shamsa's father would visit, he added.

But Essabri was sent to a boarding school in the UK after two years in Dubai.

He said he spoke to Shamsa over the phone two weeks before the letter was sent, and she told him she was miserable and wanted to escape.

Essabri said he discouraged her, and he spoke to his aunt, Shamsa's mother, to ask that restrictions on the teen be loosened.

Princess Latifa bint Mohammed Al Maktoum tried to escape last year. [Image: BBC]

He claims his name was taken off deeds and his allowances were cut off.

In a separate interview, Essabri told Australia's 60 Minutes programme that he fears Shamsa and Latifa are in danger.

He added: “There’s no freedom. If I had stayed there, if I had been kept there, I don't think I could have survived.”

Meanwhile, Oxford-educated Princess Haya, 45, one of the sheikh’s six wives, is in Britain after she allegedly fled her husband, who is friends with the Queen, with her two young children.

A two-day court hearing relating to the couple's children is due to take place on Thursday and Friday in London.

Haya is the half-sister of Jordan’s King Abdullah.