But just hours after The Sunday Times published their story, Mr Johnson denied he had admitted to dying his hair.
Tim Shipman, political editor at The Sunday Times, posted on Twitter that the Conservative contacted him to say he "thought I was joking about hair dye and that he was joking too about using it."
A spokesman for Mr Johnson told the Standard: "Boris was joshing with him - of course he doesn't dye his hair."
Mr Johnson’s former MP father, Stanley Johnson, previously suggested his son’s hair colour was completely natural.
He said: “I can tell you that’s 100 per cent.
“I remember when he was born in New York, I nipped off to get a pizza and when I returned he was swaddled with all the other babies – but quite distinguishable by his shock of white hair.
“So I can reassure the nation, it’s quite genuine.”
But top hair stylist Heinz Schumi said he believed Boris reached for the dye some years ago.
He said: "I went to see him give a speech and when the spotlights shone on his hair, it was kind of orangey - it doesn't go light enough."
