Derek Rose, 33, of Camden, north London, has been found guilty of blackmailing model and socialite Tamara Ecclestone at Southwark Crown Court.
Rose was in a relationship with the daughter of Formula One supremo Bernie Ecclestone when she was just 17.
Rose, 33, went out with Ms Ecclestone, 28, in 2002 before he changed his name by deed poll from Jonathan Ketterman.
Southwark Crown Court heard that Rose and media studies student Jakir Uddin, 20 - whom the jury have yet to deliver a verdict on - plotted together to blackmail Ms Ecclestone and drafted an email together which they sent to her manager, Dana Malmstrom.
Rose, of Arlington Road, Camden, London held his head in his hands when the jury announced the guilty verdict.
The 11-strong jury, which had been told it must reach a majority verdict of 10 to one on Uddin, was discharged after it could not agree on a verdict on Uddin.
In a note to the judge, the panel said: "We are still undecided and can not meet a majority verdict. We feel certain further deliberation will not change individual decisions."
Uddin was bailed and will appear for a mention on 25 March.
The email was sent on 16 November 2011 after Ms Ecclestone had starred in Billion Dollar Girl, a reality television programme exploring her life as a rich youngster, and after she had generated publicity in charity campaigns.
William Boyce QC said there were several drafts of the email constructed to "choose the right words to pressure and intimidate Ms Ecclestone into paying £200,000".
The barrister said the email went on with "pernicious" implications about damage to Ms Ecclestone's reputation.
Part of the email was written in bold but not read out in court.
It referred to an "incident".
The tone of it was "you don't really want that in the press whether it's true or not", said Mr Boyce.
Rose was bailed for sentencing at the same court at 10am on Tuesday morning.
Judge Andrew Goymer said it was: "Nothing more than a civilised and humane opportunity to set your affairs in order and say goodbye to your family before you face the inevitable prison sentence."
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