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The romance, which she claims lasted between 2012 and 2016 - when Boris was the Mayor of London - took place whilst he was married to his second wife, Marina.
Arcuri alleged that the pair had a 'physical and intellectual attraction' but says that in the end he was a 'cowardly wet noodle' because he refused to stand beside her in a row about her travelling on foreign trade trips with him.
The businesswoman claims that the pair had a 'physical and intellectual attraction' and bonded over a love of Shakespeare.
She also told how she codenamed him 'Alexander the Great' in her mobile phone, a reference to his full name - Alexander Boris de Pfeffel Johnson.
Questions have been asked about the pair for a few years now after the 35-year-old travelled on three trade trips led by 56-year-old Boris and funded by the UK taxpayer.
This is the first time that Arcuri has said on record that the pair were in a relationship that was more than just friendship.
Speaking to the Sunday Mirror, she said: "We were in an intimate relationship for four years. I loved him, and with good cause. But the man I thought I knew doesn't exist any more."
In that interview, Arcuri also claimed that she had sex with Johnson hours before he sat between his wife and Princess Anne at the opening ceremony of the 2012 Paralympic Games, and that she had to help him find his sock lost in the heat of passion before he headed off to that event.
She also claims that she sent him a number of intimate photographs, one of which he described as 'enough to make a bishop kick a hole in a stained-glass window'.
Arcuri also stated that Boris met her in a hotel for a date, but then had to borrow £3.10 from her in order to buy a drink, and also told her 'this is my city, I don't care' when she admitted concerns about kissing him in public.
Arcuri's story could have serious repercussions for the PM, as it asks questions about Boris' use of public cash and whether he has breached a code of conduct during his time as Mayor of London.
The Greater London Authority will now examine whether he conducted himself with 'honesty and integrity', whether Arcuri was afforded 'preferential treatment', and whether he breached the Nolan Principles of Public Life which guide officials in such situations.
The probe will also investigate whether there was any conflict of interest that should have been declared at the time.
Arcuri's company hosted Johnson as a speaker at several technology events, and she also received £126,000 in public money, including a £100,000 government grant in 2019.
Arcuri maintains that she attended the trips in her own right.
Speaking about Boris' refusal to stand by her against the allegations, Arcuri added: "It's embarrassing. What a child. You can't get on the phone and say, 'Look Jen, this is crazy, welcome to politics'?
"He just took the most cowardly, wet noodle of approaches. This is who he is and it's about time we recognised that.
"A great leader is charismatic, courageous and brave. None of these words I would use to describe Boris Johnson."
However, she claims that she was not fully aware of the rules and suggested that Boris should perhaps have declared the relationship.
Arcuri said: "I would have seen no reason why he shouldn't declare me."
LADbible has contacted 10 Downing Street for a comment.
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