Duchess Catherine's cover shoot for Vogue magazine was kept secret for four months.
The 34-year-old royal recently appeared on the front cover of the fashion magazine's 100th anniversary edition and it has now been revealed that Vogue editor Alexandra Shulman kept it quiet for 16 weeks.
Richard Macer, who shot a documentary at Vogue magazine's headquarters, said: "Trust. It's a critical ingredient in any successful documentary. My job is to make the contributor feel them can speak openly and honestly in an unfettered way.
"But for some reason Alex felt she couldn't tell me about the royal photo shoot. It wasn't just a case of withholding information. She actively lied. More than that, she developed an elaborate ruse."
And Richard was impressed that Alexandra managed to get the "scoop of the year".
He added: "The centenary issue is selling like hot cakes and Alex is still at the top of her game. Far from announcing her retirement, she'd pulled off the scoop of the year."
Richard also revealed he was kept in the dark about the shoot until April 28, where the photos of the Duchess of Cambridge were revealed.
Speaking in the BBC2 documentary, 'Absolutely Fashion: Inside British Vogue', he added: "I'm told I must not discuss this with anyone, even Alex. I can't stop thinking about this surprise announcement,' he said of the longest-serving editor of British Vogue. Maybe she's going to tell everyone she's leaving.
"I think it's a surprise party for her staff to say thanks for all their hard work. I've been speculating quite a lot about what she's going to say but the truth is, I have no clue."