The Princess of Wales has been seen for the first time amid mounting pressure for the release of the original version of her “doctored” Mothers’ Day photo.

Kate was seen in a car with husband Prince William on Monday (British time), as he left Windsor Castle headed to London for the Commonwealth Day service at Westminster Abbey.

“Princess Kate was pictured sitting in the backseat of the car and looking out of the window, whereas William was looking ahead,” Britain’s Daily Express wrote.

The princess did not attend the annual service, which was led by the Queen and the Prince of Wales. Rather, she was reportedly on her way to a “private appointment”.

The brief sighting was only about the third since the palace revealed in mid-January that Kate had had major abdominal surgery and would take time off from royal duties until after Easter to recuperate.

It also came as Kensington Palace refused to release the original version of the photo of Kate with children Prince George, Princess Charlotte and Prince Louis that has caused an international storm.

The photo – apparently taken by Prince William – was released on Sunday to mark Mothers’ Day in Britain. Its caption, which thanked fans for their “kind wishes and continued support over the last two months”, referenced Kate’s time out of the spotlight since her surgery.

The happy snap followed weeks of speculation about her whereabouts and was designed to quell wild speculation and rumours. Instead, it has sparked even more conjecture.

Controversy quickly erupted as eagle-eyed royal watchers picked up discrepancies in the image. They included the absence of Kate’s wedding and engagement rings, as well as apparent glitches in clothing and the children’s hands.

Social media users accused Kensington Palace of creating an AI-generated image, or creating the image in photo-editing software.

Tweet from @chrisshipitv

The claims were lent further credibility when major photo agencies such as AP and Reuters issued “kill notices” based on their belief the image had been manipulated.

Britain’s national news agency PA reportedly had confirmation from Kensington Palace that it “would not be reissuing the original unedited photograph of Kate and her children”. It also withdrew the photo, saying “in the absence of that clarification, we are killing the image from our picture service”.

On Monday (British time), the princess took responsibility for the furore, releasing a brief – and rare – public statement apologising for the “confusion” caused by her editing.

“Like many amateur photographers, I do occasionally experiment with editing,” she wrote on social media.

“I wanted to express my apologies for any confusion the family photograph we shared yesterday caused.”

Tweet from @KensingtonRoyal

British media is reporting that the royal sources have said Kate made only “minor adjustments” to the picture, and insisted she and William simply wanted to release an informal picture of their family together for Mother’s Day.

“The Wales family spent Mother’s Day together and had a wonderful day,” one source told the Mirror newspaper.

The palace has refused to say how the photo was edited. But a Sky News analysis of its metadata revealed that it was saved in Adobe Photoshop twice on an Apple Mac and that the picture was taken on a Canon 5D Mark IV, with a Canon 50-millimetre lens. The broadcaster said the image was first saved at 9.54pm on Friday and again at 9.39am on Saturday. It is not clear if both saves were made on the same device.

The row has escalated further after the deputy news director of photo agency AFP – one of those to withdraw the picture – said it had been “badly edited” and manipulated in a way that didn’t meet its standards.

“It is a bad day at the office for the palace and something which will no doubt be reflected on in future,” a royal source told the Mirror.