The photographer who captured the car shot of the Prince and Princess of Wales didn't realise that Kate was sitting next to her husband until he looked at the image on a computer.
Jim Bennett had expected to see only Prince William as he made his way to the Commonwealth Day service at Westminster Abbey in London from Windsor.
"We do a little work in Windsor and we were asked by two publications to get an early picture of Prince William going to the service at Westminster Abbey," he explains to HELLO!
"What I didn't realise at the time was that sitting next to him, until we looked at it on a computer, was Kate!"
Jim captured the couple seated in the back of their black Land Rover as they travelled from Adelaide Cottage to Windsor. HELLO! understands that the Princess, who is still recuperating from having abdominal surgery, had a private appointment in the capital.
"The only reason we shot William was because he was going to a job. We'd been given the green light to do that because he was travelling on to Westminster Abbey," Jim says.
The outcry over the Mother's Day photograph of Kate with her children has heightened speculation over other images of the royals, including Jim's car shot.
When asked about its authenticity, Jim tells HELLO!: "I've been a photographer for over 40 years, it was important to us because we were asked to get a picture of William, which we did, albeit not the best picture.
"On a scale of one to ten, it's probably the worst picture I've done in ten years, car-shot wise. A situation arose, it had to be grabbed very quickly. If I had taken a proper picture, a good quality picture, looking at that there is no way I'd put a picture out as bad as that if I didn't think it was important.
"The picture of William was good enough, it just so happened that [Kate] was sitting to the side of him even though you can't make her out clearly, you can see she's looking away and it was only the confirmation by their press office that they confirmed that she was in the vehicle with him."
Hours after it was released by Kensington Palace, the Mother's Day portrait was "killed" by news agencies because of suspicions it had been digitally altered.
Concerns were raised over a missing part of Princess Charlotte’s sleeve and the misaligned edge of her skirt, with other queries including the positioning of Kate’s zip.
On Monday, Kate issued a statement via social media, saying: "Like many amateur photographers, I do occasionally experiment with editing. I wanted to express my apologies for any confusion the family photograph we shared yesterday caused. I hope everyone celebrating had a very happy Mother's Day. C."
Talking about the downside of editing with Photoshop, Jim says: "It is a bit addictive, Photoshop, for everybody. I'm a great aficionado of Photoshop, crop my pictures, I lighten them and darken them, and I send them to the newspapers, that's the end of it for me.
"I could see that somebody that's a keen amateur with the opportunity to play around, it's very addictive. And I'm assuming that's what [Kate's] done. She should've had a little bit more guidance from a professional photographer because they would have spotted there was a problem immediately."
Jim adds: "[As photographers] we're not allowed to do it - we're not allowed to manipulate any pictures apart from a little bit of lightning, a little bit of darkening and that's it.
"To literally change the content, you can't do that. If you're a professional, you don't, end of story, it's a rule that's laid down by everybody, which is a reason why it got pulled."