She was the richest heiress in the land – a stunning, curvy 21-year-old with a designer wardrobe and a £4million-a-year property empire.

He was a dashing, sports-mad hunk related to a national hero, whose partying and shameless sexploits got him nicknamed Mr Long Pole.

The public couldn’t get enough of Catherine Tylney Long and William Wellesley Pole, and when they tied the knot in a media frenzy they became megastars.

But this wasn’t Hollywood 2015 – it was London 1812, and these glamorous newlyweds were the first ever celebrity couple.

Regency England’s version of Brangelina, Kimye and TomKat filled the gossip columns for more than two decades – and the OMG! scandals of “Catiam” would break the internet today.

There was love, passion, adultery, betrayal, obscene wealth, bankruptcy, exile, shame, a salacious divorce trial and finally a child custody case that would change legal history.

Much-loved Catherine, nicknamed The Angel, even turned down a marriage proposal from the future king to marry William, 23.

But the handsome nephew of the Duke of Wellington turned out be a feckless philanderer, and within 10 years he’d broken her heart, blown her fortune and moved his mistress into their home.

Yet when he attempted to deprive Catherine of her three children, she defied convention and fought him for custody.

She was a brave, feisty heroine who could have stepped from the pages of a Jane Austen novel, yet for decades the history books have portrayed Catherine as a foolish, feeble woman.

Only now, 200 years later, is she finally getting the recognition she deserves, thanks to a new book called The Angel and the Cad – Love, Loss and Scandal in Regency England.

Author Geraldine Roberts spent 10 years painstakingly researching the twists and turns of Catherine’s extraordinary life after discovering a box of her letters in an archive.

Mum-of-two Geraldine, from East London, says: “It sounds corny, but it felt like fate, as if I was meant to tell her story.

"Catherine had been portrayed as stupid and foolish – hey, she could have been Queen of England but she married the wrong man and ended up ruined.

“But from her letters it was clear this was a very clever, witty and caring woman who made a huge contribution to women’s rights.

"She is a true unsung heroine and I felt I had to salvage her reputation.”

Geraldine’s detective work and vivid storytelling make the Angel and the Cad a racy, poignant read and the parallels between this 19th Century saga and today’s celebrity culture are fascinating.

Catherine was an ordinary girl from a loving home who, at 16, inherited a £40,000-a-year fortune from her wealthy uncle – £4million in today’s money – as well as 23,000 acres of land in six counties and several stately homes.

She was propelled into a dazzling, decadent world – like a teen lottery winner today – but remained so unpretentious and sweet-natured that the media and public adored her.

She was distantly related to author Jane Austen, and inspired the heroine Catherine Moreland in Northanger Abbey. She was pursued by suitors including the Duke of Clarence, later William IV, but fell for William.

Geraldine calls him a cross between Heathcliff from Emily Bronte’s Wuthering Heights and Mr Darcy from Pride and Prejudice, and says if ever her book becomes a film Poldark’s Aiden Turner is perfect to play him.

The press loved to hate William, and cartoonists – the paparazzi of the time – portrayed him as Cock of the Walk and saucily dubbed him Mr Long Pole.

Geraldine says: “William was driven by his libido. Illicit thrills were like a drug to him and it is possible he had a sex addiction. Everyone wondered what would happen to the sweet heiress when he married her.”

Their London wedding in 1812 was more lavish and widely followed than the 2011 wedding of that other William and Catherine. The bride wore diamonds worth £5million and her gown started the fashion for white weddings.

The couple even merged their names to become Mr and Mrs Pole Tylney Long Wellesley... but would no doubt be Catiam today.

“They lived like royalty at Wanstead House in Essex,” says Geraldine.

In the days before Twitter, TMZ or celebrity mags, the educated classes were also involved in social networking – exchanging gossip through letters and notes.

“They delighted in the latest scandal, describing acquaintances in acid detail,” says Geraldine.

Like many modern celebrities Catherine also had a stalker – who turned up on the doorstep with a carving knife and had to be restrained by servants.

William’s extravagance became notorious as he hosted glittering parties for the Duke of Wellington, the Prince Regent, Beau Brummell and Lord Byron.

He gambled constantly and kept a stable of the finest horses – the equivalent of a garage full of top-of-the range cars.

But within a decade, he had squandered his wife’s enormous fortune and was made bankrupt.

Wanstead House was stripped bare before being demolished and sold for scrap. William fled to the continent to escape debtors’ prison.

Loyal Catherine refused to abandon him and took their three children to join his exile in France and Italy. But William didn’t change.

He hired a pimp to find him prostitutes, took a mistress and moved her into the family home in Naples.

Geraldine adds: “Catherine wanted a divorce but English law stipulated that a father had ultimate parental control.

"William made clear that if she left him she’d never see her children again.

"Catherine finally made a stand when William started to harm the children. With the help of family she took them back to England and went into hiding.

"William pursued her relentlessly, hiring armed thugs to seize the children.”

Catherine became worn out with worry and began suffering chest spasms. She died in 1825, a month before her 36th birthday, and the tragedy prompted a public outpouring of grief similar to that following Princess Diana’s death.

But Geraldine discovered how the Angel finally beat the Cad... from beyond the grave.

She says: “Before her death, Catherine approached the Lord Chancellor and made a strong case for custody of her children, William, 12, James, 10, and Victoria, seven.

“The children were made wards of court, and the Duke of Wellington became their guardian.

“Catherine had prepared her argument so well that the landmark trial went ahead after her death.”

The newspapers were full of salacious details of William’s adultery, and Catherine’s celebrity status added to debate. Finally the judge ruled in her favour.

“William became the first man in England to be deprived of his children on the grounds that he was an unfit parent – a revolutionary concept,” says Geraldine.

“The case changed the law regarding child custody. But the Victorians didn’t like strong women so they airbrushed her out of history.”

William married again in 1828, but abandoned his second wife for her maid. He died in 1857, aged 70.

Geraldine says that when William was younger there were flashes of real humanity and genius, and he did some very generous things.

“It was the flashes of recklessness that ruined him,” she explains.

“But it’s Catherine who has to have the last word. Because she won in the end.”