As a 14th birthday treat, Lady Elizabeth Bowes-Lyon was taken by her parents to a West End show, to see Sir Charles Hawtrey at the London Coliseum. On the same day her future father-in-law King George V summoned the Privy Council and declared war on Germany.
It was a defining moment of the century, and in the life of the Strathmores. Elizabeth's three eldest surviving brothers Patrick, Jock and Fergus (another, John, died young in 1911) hurried to rejoin their regiment, The Black Watch.
A fourth brother, Michael, abandoned his studies at Magdalen College in Oxford and immediately enlisted in The Royal Scots. The war, after all, would be over by Christmas.
The London house was closed up and the family retreated to Glamis, where estate workers were flocking to enlist, in happy ignorance of their fate.
Before embarking for France, two Bowes-Lyon brothers dashed to the altar - John marrying the majestically named Fenella Hepburn- Stuart-Forbes-Trefusis, and Fergus settling for plain Lady Christian Dawson-Damer.
Lady Strathmore opened Glamis as a convalescent hospital, equipped with 16 beds, although she had to wait until Christmas for her first patients, invalided home from the Western Front. Elizabeth became the hospital dogsbody, her first tasks being to knit comforters and crumpling up tissue paper as lining for sleeping bags.
In September 1915 Fergus came home on leave to see his two-month-old daughter for the first time. Three days after his return to France he was killed in action at the Battle of Loos.
The news caused Lady Strathmore to collapse. She effectively withdrew from her hospital, leaving its running to her daughters Rose, a qualified nursing sister, and Elizabeth. For a young teenager born to privilege, it was an experience both humbling and levelling, as for the next four years she gave the wounded her unqualified attention.
She had no formal nursing training, but she wrote their letters, fetched their tobacco from the village shop, played them at whist (at which she almost invariably won) and led them in sing-songs.
Most of all she talked to them, becoming to the men a surrogate wife, daughter or sweetheart.
She maintained their spirits with her sense of fun, on one occasion dressing up her younger brother as a girl and introducing him as her long-lost female cousin around the oak-panelled dining room which served as the ward.
The First World War was the great leveller, and at Glamis and elsewhere, British society would never be quite the same again. On the annual castle Christmas tree, laden with presents for friends and family, there was always a gift for every soldier.
Between times, Elizabeth raised funds for the Red Cross, ran the local Girl Guide troop, and even had time to deal with a fire in the castle. Spotting the flames, she telephoned the Glamis fire brigade while organising a human chain to pass out the valuables.
When the firemen arrived they found their hoses too short to be of the slightest use. But Elizabeth had thought of everything - she had also called the long-hosed Dundee city brigade, who arrived in good time to avert certain disaster.
The death of a son in action had cast a heavy pall over the Strathmores, as it did over countless homes of every social class throughout the land.
Early in 1917 came news that another Bowes-Lyon boy, Michael, had also been killed. But the report was false and after an agonising three months word reached Scotland that he had been found alive in a prison hospital in Germany.
Amid the bleakness of war there was an outburst of rejoicing at Glamis and an even greater one when, after a seemingly endless wait for his repatriation, he turned up at Dundee railway station one fine day in 1919.
Many years later, Queen Elizabeth would find a particular poignancy in being invited to become Colonel-in-Chief of The Black Watch, with her granddaughter Anne in the same honorary position with The Royal Scots today.
For the latter part of the war, Elizabeth, still a girl of barely 17, found herself more or less in charge of the hospital. Her mother was still deeply affected by the loss of Fergus, and Rose had found a diversion, marrying William Leveson-Gower.
She coped manfully, buoyed by an impish sense of humour, an easy manner and a belief that the ghastly war must end sooner or later and people could get back to dancing. Those were the years in which Elizabeth grew up from sunny, happy-go-lucky child to worldly adult.
It was 1919 before the last of the patients left Glamis, piling the Strathmores - and Elizabeth in particular - with parting gifts. As the last of them disappeared down the long castle drive, the words of Goodbye Dolly Gray wafted back on the breeze.
Normality returned as the aristocratic familes resumed the threads of their prewar life in what was a changed world. But life's milestones still had to be observed: in 1919 Lady Strathmore held a coming-out dance for Elizabeth, at which the girl could display her impressively elegant footwork and signal her availability on the upper-crust marriage market.
The growing-up of Elizabeth was complete. She had become a debutante, launched fully fledged into the vibrant beginnings of the Jazz Age.