British diplomats pride themselves on retaining their sangfroid even at the most historic of moments, and so it was with Tim Barrow, Britain's permanent representative to the EU, when he left his office yesterday morning.
Were it not for the polyglot camera crews chasing him to his official Jaguar, demanding to know about the contents of his battered leather satchel, it could have been just another day in the office.
It was 8.45am in London and Mr Barrow was departing at his usual time for a routine meeting with his fellow EU ambassadors; but this was no routine day, it was the moment when Britain formally declared its intention to leave the European Union.
As the UK prime minister's official messenger, Mr Barrow was careful to let his boss back in Westminster do the talking, striding impassively to his car where he remained cocooned from further demands for information for the 400-yard drive to the European Council building.
Mr Barrow has kept a low profile since coming to Brussels to replace his more loquacious predecessor, Ivan Rogers, and on arrival, he let slip only a breezy "morning" as he swept into the bowels of the European Council's giant new headquarters, popularly known as "the egg".
A flash of crimson from the lining of one of Mr Barrow's impeccable Savile Row suits - for which he is renowned in the diplomatic corps - was perhaps the only concession to his walk-on part on this historic day.
After nine months of speculation about the contents of the Article 50 letter, the world was then forced to wait just a few more hours, while the ambassador sat in his meeting with soon-to-be former colleagues.
In the interim, Twitter filled up with jokes about the perils of letters getting mixed up - think the Oscars - and questions about why his briefcase, with its faded official coat of arms, was not manacled to his wrist.
Across Europe, the morning newspaper editions also had their say. France's 'Liberation' declared that "we miss you already", emblazoning the message against a British Guardsman's bearskin; while 'Die Welt' pictured Mrs May alone at sea in a Union Jack paper boat, adding it was not too late for Britain to reverse course. "Ze door is schtill open," joked the cod-English headline on its front page.
History does not yet relate if Mr Barrow handed the precious letter to a colleague for safekeeping, or kept it under his chair - checking nervously every few seconds to ensure it was still there - but the ambassador could have been forgiven if at times his mind wandered away from the business in hand.
It was an agonising four hours later- 12.45 in London - that Mr Barrow was finally able to deliver the letter into the hands of Donald Tusk, the European Council president. The moment was recorded only in an awkward still photograph, in which a grim-faced Mr Tusk is seen taking the letter gingerly in two hands, as if it were a bomb about to go off.
It was an emotional Mr Tusk who addressed the world some minutes later, expressing genuine sadness that Britain was leaving a union that was formed a month before his own birth in April 1957.
That was a sentiment echoed to varying degrees across Europe. Mariano Rajoy, the Spanish prime minister, said it was a "disappointing" day for Europe while Joseph Muscat, the Maltese prime minister, who holds the rotating EU presidency, said that Brexit was a "sad day" and marked "a big leap into the unknown for everyone".
But it did not take long for the gulf between the two sides' expectations to emerge.
Within hours Angela Merkel was challenging Mrs May's determination that the UK wants to negotiate a future trade agreement at the same as it agrees the terms of its "divorce", including settling the euros 60billion Brexit bill.
Francois Hollande, the French president, said that he believed Brexit would be "painful" for Britain, while Valerie Giscard d'Estaing, the father of the defunct European constitutional treaty, dismissed Brexit as "not a worry" for the eurozone and predicted that Britain will be the "main losers" from the divorce.