Miss DeFalco, 41, a Miami-based escort who charged up to $2500 (£1500) for sex, said she “broke all the rules” for the British playboy, 37, after he answered one of her internet advertisements in April 2004.

Wooing her with champagne, roses and claims he was a “James Bond” type who spied for the American and British governments, Papalexis soon became infatuated with the former hardcore porn star, after they met for sex in luxury hotels in Florida.

Miss DeFalco, who had travelled to London to give evidence at Papalexis’ murder trial, said their three-month relationship became “turbo charged” after she “fell under his spell” from a series of confessional love letters.

“He was charming. He was someone I broke all the rules for,” Miss DeFalco told the Old Bailey during her evidence at Papalexis’ murder trial.

“I was fooled, I was mesmerised and I was charmed. Every part of me and all of my senses were completely involved.

“I fell hard. I was taken for a ride. I was completely smitten.”

Papalexis, who had become a member of the “Palm Beach elite” after leaving Britain shortly after committing murder, became obsessed with her and had asked her to give up other clients for him and started paying her $2500 in lump sums.

He even paid DeFalco, who starred in porn movies with actor Ron Jeremy, to have sex with other men while he watched and also filmed their encounters.

The court heard that she was one of several woman Papalexis cheated on his wife, Karina, with. He even paid for cosmetic surgery for four women, the court heard.

He claimed she had agreed to let him have "discreet" sex with other women after she suffered problems during fertility treatment.

The court was told he had hosted “wild sex parties” at his rented mansion and joined a sado-masochistic pornography website, all of which helped satisfied his “insatiable” appetite for sex.

It was his relationship with the prostitute that appeared to have played a major part in the businessman’s downfall.

The court was told Papalexis told her he worked for the CIA, MI6 and the US national security agency before “confessing” during a heated row at the Four Seasons Hotel in Palm Beach to murdering a “nobody”.

The court had heard Papalexis had Charalambos Christodoulides, 55, murdered because he refused to move from the £2million North London building Papalexis had been trying to sell to help pay debts.

The recluse had been tied to a chair, beaten, tortured and strangled at the Kilburn site.

During a heated row between the pair Papalexis claimed he had murdered the caretaker because he “had got in the way”.

In a fit of rage, she asked him “have you ever killed anyone”.

“(He replied) ‘yes I strangled someone,” she told the jury.

“This man was giving me problems. He said he was in the way.”

But Paplexis told the court he falsely told her he loved her and that he spun an elaborate fantasy to Miss DeFalco during an intense sexual relationship.

“I wanted her to feel loved and to feel that I was a super-spy and that we would have great sex and great fun together,” he told the court.

“I have regaled her with stories which would make a screenwriter envious - but I have never mentioned anything to do with this murder.

"I told her about missions, explosions, car chases, gun battles in the desert, stories that you would see in a movie but nothing to do with the murder of a 55-year-old gentleman in a warehouse in London."

So convincing was his act, the court was told, that after Papalexis “disappeared”, she wrote to then US President George W Bush asking for help.

Later he admitted making a number of lies to the prostitute including killing the caretaker and pretending that a cross and a set of rosary beads had been removed from the hands of his dead mother after her body had been exhumed from its grave.

In fact, he admitted he bought it in a shop years before.

Prosecutor Jonathan Laidlaw, QC, told the court that Miss DeFalco said nothing about the confession until she read about his arrest in December 2008.

She then came forward after “everything that man told me came back”.

Later, after resuming email contact and revealed she was fighting cancer, he simply replied: “Bon Voyage.”