Daily Mirror editor Richard Wallace today expressed "regret" and admitted the paper "got it wrong" over a paparazzi photograph of Kate Middleton published yesterday.
Lawyers for Prince William's 25-year-old girlfriend complained to the Press Complaints Commission (PCC) yesterday about a photograph of her walking to work.
Wallace said: "The Daily Mirror has always steered a sensible course in the use of photographs of Kate Middleton and other public figures.
"On Thursday we published an innocuous picture of Ms Middleton walking down the street with a cup of coffee.
"It was taken by a freelance photographer in circumstances where we were later told she felt harassed.
The story was headlined "Look out, Wills here comes an heir-bashing" and was captioned "SMOULDERING: Kate leaves for work yesterday".
Middleton made the complaint through her lawyers Harbottle and Lewis after making several informal complaints in recent weeks.
The complaint is under clause four of the PCC editors' code of conduct which prohibits harrassment.
The complaint will be heard by the PCC on 1 May. A result is expected the same day.