In June last year she disguised herself so as to attend one of the pop star's concerts in Paris, the book claims.
The biography also claims Emmanuel penned a racy novel inspired by their early romance.
He is said to have stormed out of the family home and was incandescent with rage over the relationship.
Emmanuel Macron also happened to be a school friend of the Auziere's daughter, Laurence, at the time.'When [Brigitte's] husband learns the truth, his reaction is violent,' writes Brun.'To be replaced by a schoolmate of his daughter, by an adolescent whom he had often received at his home?
'But she has sometimes told me she lost all her friends,' the acquaintance went on.
Maëlle Brun's unauthorised biography, titled 'Brigitte Macron: L'Affranchie (The Unfettered Woman)', has hit the shelves as President Macron lands in Britain today for his first visit since moving to the Élysée Palace'Friends with whom she went on holiday changed overnight and no longer wanted to speak to her.'Brun adds that tensions ran 'extremely high' at the time of the relationship.
Their affair ended Mrs Macron's marriage to Andrew-Louis Auziere, now 66 - though she did not get divorced until 2006 - and led to Mr Macron being removed from the school and sent to Paris.
Auziere had a 'violent reaction' when he heard she was having an affair, the biography claims.
That's a difficult wound to heal.'Mr Auziere was working in finance at the time, and had been enjoying a happy life with his wife and three children in Amiens.'And the banker did not procrastinate – he leaves,' the book explains, quoting an old neighbour as saying: 'He was not seen again.
It was as if he had disappeared.'The book continues: 'He took it like such a slap. I think it wasn't easy to see the children appreciating Emmanuel afterwards.'There have been next to no public sightings of Mr Auziere since that fateful day in September 1996, and it was a full ten years before their divorce was finalised.
Now the first lady of France, Mrs Macron shocked locals in Amiens when details emerged of her relationship with the future president.