Boris Johnson has always been ambivalent to Brexit, despite fronting the Leave campaign this summer.
This is according to The Guardian journalist Dave Hill, who is writing a biography on the Conservative politician.
Hill was speaking after Sir Alan Duncan told the BBC yesterday that the Foreign Secretary didn't want the Leave campaign to win the referendum vote.
Hill, who has followed the former London Mayor for eight years while researching his biography, explained his view of Johnson's position.
"I think he's always been rather ambivalent," he told Julia Hartley-Brewer. "What Alan Duncan said on the BBC documentary (Brexit: A Very British Coup) yesterday was that Boris decided to join the Leave campaign [because] it served his interests to become the leader of the Conservative party.
"To do that, you have to be popular with the grassroot voters, who are very eurosceptic. But they love Boris, viewing him as being quite eurosceptic despite him being regarded generally as fairly europhile.
"He wasn't particularly anti-Brussels, but he had a clever way of speaking to that frame of mind, and part of his appeal is the mischief factor."
Earlier today Johnson said the process of separation from the EU is likely to begin next year.
Click on the audio above to listen to the interview