Clarence House and the Sun have clashed over whether an Army cadet filmed at Sandhurst by a reporter who constructed a fake bomb was Prince Harry.
The Sun says its footage shows Prince Harry was at Sandhurst
Royal aides said the cadet pictured looked like the prince but was not him.
But the Sun said: "The footage is Prince Harry. We stand by it 100%. The Clarence House denial is absurd."
A security review was ordered by Defence Secretary John Reid after the reporter used fake details to enter Sandhurst and walked around for hours.
After the story appeared on the Sun's front page Clarence House said: "Having reviewed the footage and spoken to those who were with Harry we are of the opinion that it is not him in the footage."
BBC Royal Correspondent Peter Hunt said it was understood that Prince Harry had also seen the video and did not believe it was him.
Clarence House said the cadet in question was filmed going into New College and Harry had no reason to be there and was not scheduled to be there on the day the journalist was present.
And a Ministry of Defence spokesman later added: "I can confirm that Sandhurst are categorically saying it isn't Harry."
The Sun's managing editor Graham Dudman said its actions had been intended to "expose, for the public interest, gaps in security".
The newspaper said its reporter posed as a "warfare student", arranging an appointment at the military college to carry out research on the causes of the Gulf War.
He was waved through security and strolled into the library before wandering off, the paper said.
He later went back to his car where he constructed a fake bomb with wires, modelling clay, a battery and clock.
'No hard feeling'
Defence Secretary John Reid said there was "no excuse" for the lapse in security that allowed the reporter into the military academy.
The defence secretary said the Sun had "done us a service" after the stunt and ordered an investigation into the "serious security breach".
Sandhurst is the army's most prestigious academy
"There are no hard feelings against the Sun - they've revealed a lapse here so let's find out what went wrong and put it right quickly," Mr Reid told BBC News.
The Ministry of Defence confirmed Sandhurst was conducting a security review and would be "implementing any changes we feel are necessary".
In the past two years the Royal Family's security has been breached by a stand-up comedian dressed as a female Osama bin Laden; a Daily Mirror reporter posing as a footman; and a campaigner wearing a Batman outfit.
A review of royal security last year concluded that the most likely source of "insider threat" was from the media and individuals.
It said any weaknesses which could be exploited by them could also be exploited by terrorists.