The image appeared during the news review segment on ITV’s This Morning when the publication of the photographs of pregnant Kate in a bikini on a private Caribbean holiday was being discussed.
The photos, which have been condemned by St James's Palace, were published today by Italian magazine Chi. One of them shows Kate's very slight baby bump as she stands in the sea and is accompanied by the headline "the belly grows". Another shows the Duke, wearing a pair of shorts, with his left arm around his wife as they walk along a beach on the island of Mustique.
Presenter Holmes said: "Earlier during today's news review we were discussing photographs of the Duke and Duchess of Cambridge on a beach in Mustique published in an Italian magazine.
"Unfortunately we accidentally showed an unblurred image of the magazine cover, which briefly showed the photographs.
"This was a deeply regrettable error and we are very sorry. We apologise unreservedly to the Duke and the Duchess."
This gaffe comes just months after This Morning presenter Phillip Schofield was roundly criticised after he confronted David Cameron with a list of alleged paedophiles.
He handed the Prime Minister a list of names which he said he had put together from internet rumours - it was understood to be Conservative Party figures - during the live show.
ITV apologised on the next day's show and emphasised it was not pointing the finger at anyone in particular. Schofield was later forced to apologise after the list was briefly exposed on screen.
Broadcasting watchdog Ofcom launched investigations into This Morning's November 8 edition after complaints that it - and BBC's Newsnight - breached "generally accepted standards".
The November 2 Newsnight wrongly implicated a Tory politician in a historic paedophile ring that targeted children at a care home in Wrexham in north Wales.
THE publication of the pictures of the Duchess of Cambridge has been condemned by St James's Palace.
A spokesman said: "This is a clear breach of the couple's right to privacy."
Chi – owned by former Italian Prime Minister Silvio Berlusconi – last year caused outrage when it produced a 26-page special showing Kate topless during a holiday in France.
The Duchess's pregnancy has already been plagued by controversy after a prank radio call at the hospital where she was being treated for extreme morning sickness led to the suicide of a nurse.
Meanwhile, the editor of an Australian magazine has defended her decision to print photographs of Kate in a bikini, saying her readers will "love" the images.
Woman's Day is the second publication to use the pictures of the pregnant royal, following magazine Chi.
They were reportedly taken from a boat using a long-lens camera, but Fiona Connolly, editor of Woman's Day, claimed a member of the public snapped the Duchess.
Speaking to Australia's Channel Nine network ahead of publishing the pictures in Monday's edition of the magazine, Ms Connolly said: "This is not a hard decision about these photos. Kate's on a public beach, there are other holiday-makers there and she looks fabulous."
She made a distinction between the new pictures and those taken while Kate was topless on holiday in France last year as the latest ones were not taken at a private location.
"Look, I think the British are very sensitive about this," Ms Connolly told Channel Nine.
"As Australians, we see this every day. We see pregnant women in bikinis on the beach - and a public one at that - so we are a lot less sensitive here in Australia."