Gordon Brown was holding the packed conference hall in the palm of his hand as he heaped praise on a beaming Tony Blair sitting just feet away in rapt attention.
Delegates applauded enthusiastically as Mr Brown publicly buried his differences with his old friend. Meanwhile, in a dark corner of the hall, a silent BlackBerry mobile phone belonging to a member of the assembled press flashed a message that threatened to destroy months of work that had gone into the Chancellor's conference speech.
Cherie Blair had passed a television monitor showing Mr Brown's tribute to her husband and reportedly blurted out the damning words: "Well that's a lie" before storming out of the building.
The four words, news of which spread swiftly among the press corps, spoke more eloquently than the hour-long speech about the true relationship between Britain's two most powerful men and shattered the surreal air of peace.
It seemed almost incredible that, after so many years in the public eye, the Prime Minister's wife could so carelessly allow her private feelings to get the better of her in such a public setting. Perhaps because she was in the near-deserted exhibition hall while almost everyone was watching Mr Brown in the main auditorium she thought there would be no one to hear her, except for the stewards and bodyguards who could be counted on to be discreet.
Unfortunately for her, she was walking past a producer for Bloomberg news agency. By 12.56pm, as Mr Brown was soaking up the applause and his admirers were gathering around the television cameras to declare how well he had done, Carolin Lotter's account of Mrs Blair's outburst was already running on the news wires.
One close ally of Mr Brown struggled to conceal his fury: "In the great scheme of things it is a strange situation when the personal vision of the man who will be Britain's next Prime Minister has been overshadowed by this." Downing Street insisted that the story was "totally untrue" and demanded that it be withdrawn.
Last night, the American academic Irwin Stelzer, whose close relationship with the media mogul Rupert Murdoch gives him privileged access to Downing Street, was overheard in the conference relaying a version of events that presumably came from Cherie Blair or someone who was at her side when the disputed remark was uttered. His version was that she actually said: "I must get by."
Jaws began dropping as senior Labour figures got wind of the incident. As news of Mrs Blair's alleged remark was broken to her, one senior minister's face simply froze. Meanwhile, reporters besieged the Radisson Hotel where Mrs Blair and the rest of Labour's high command are staying. A phalanx of press officers deployed crowd barriers to keep the crush back and Mrs Blair's driver tried to fool waiting reporters. A planned shopping trip by Mrs Blair was summarily abandoned.
As senior ministers walked into the conference hotel, the alarm in their voices was evident. "I think we have walked into something we didn't want to walk into," muttered Alistair Darling, the Transport Secretary.
Inside the hall, senior figures in the party were thinking the same thing.Reuse content