It could have been the sunshine but a suspicious pink glow spread across the face of the Taoiseach as he talked about an evening spent in the company of the Princess of Wales.
Mr Ahern was speaking yesterday morning outside the British embassy in Dublin after signing the book of condolences.
"God Bless Diana" he wrote in the leather-bound book.
Outside, reporters pressed him for his memory of the princess.
"Well, that would have to be the time I met her," he said with a smile. It was December 1992, at a dinner for the conclusion of the European Summit where £7.84 billion in EU cohesion and structural aid had been agreed for Ireland.
Mr Ahern, then Minister for Finance, had been lucky enough to be seated near the princess on the royal yacht off Edinburgh.
"Princess Di", he recalled yesterday, was the "hit of the night". He was asked whether he managed to have a quick word. The Taoiseach assured his questioner that in fact he had enjoyed "more than a quick word".
He said Prince Charles had been giving him a rough time. The prince told him that he had been to every country in the world except Ireland and wanted to know when the political situation would be stable enough so that he could visit.
"We were all talking about it. I told them I hoped for the day it would be more peaceful," said Mr Ahern.
Mr Ahern was impressed by Princess Diana's "warmth and charm and a tremendous personality", he said. The grief of Irish people reflected the "high esteem" in which the princess was held.
"I was in Croke Park over the weekend and at the U2 concert and I was struck by the feeling of shock and sadness about her death," he said.
The last correspondence the Taoiseach read before he left his office on Friday night was a letter sent by President Clinton concerning a subject close to the princess's heart.
In the letter, which was sent to 99 other countries, Clinton said that the United States would support a worldwide ban on the production, export and use of antipersonnel mines. A conference on the issue, to which the princess had been invited, began in Oslo yesterday. "Last night I couldn't help thinking that people have been trying to do something about the landmines for 35 years. It took someone like Diana to take an interest before anything happened," Mr Ahern said.