Mary Stewart departed for France on the 28th of July, 1548. (N.S. 7th of August, 1548).
Lang Mary Stewart left Scotland for exile in France as the six years old Mary I, Queen of Scots. During her thirteen years in France, Mary Stewart became Marie Stuart, was betrothed and later married to the Dauphin, became Queen Consort of France for a wee while as the wife of François II, upset Elizabeth I of England, and lost her husband. That latter became something of which she made a habit, but that's a story for another day. Mary sailed from Dumbarton on the 28th of July, 1548, accompanied by a fleet of French ships and arrived a week or so later at Saint-Pol-de-Léon. She was accompanied by her own court including the 'four Marys' (Beaton, Seton, Fleming, and Livingston) and a governess, Janet, Lady Fleming.
Mary Stewart was the only surviving legitimate bairn of King James V of Scotland. She was born
when her father was in his sick bed and only six days old when James V died. Mary became Mary I, Queen of Scots, on the 14th of December, 1542, but she wasn't crowned until nine months later, on the 9th of September, 1543. As Queen Regnant of Scotland, she ruled in her own right, with all the sovereign powers of a monarch, albeit she was absent for a while and always more in theory rather than practice. As Queen Consort of France, Mary shared her husband's rank and held the feminine equivalent of the monarchical titles of François II, but she didn't share his political and military powers, not that he had any, in truth. As potential heir to the throne of England, Mary also shared the ambition of François II or rather his father, Henry II, and her uncles, the Guisers, brothers of her mother, Mary of Guise, whom she'd left behind in Scotland as Regent.
That ambition was, in effect, the unification of the thrones of France, Scotland and England, and Mary's marriage to the Dauphin who became François II was arranged with that outcome in mind. That was more than a wish list item, it was a distinct possibility at the time. Previously, under the Treaty of Greenwich, signed on the 1st of July, 1543, between England and Scotland, Mary had been promised to Edward, the son of Henry VIII. The Prince and Princess were to have married when Mary was ten and the canny Scots made sure that if the couple failed to have children, the proposed union of the two countries (as it then was) would dissolve.
However, Henry VIII reckoned without Cardinal Beaton, a worthy adversary and protector of Scotland in many folks' eyes (a Catholic and a sinner in the eyes of those who later murdered him). Unsurprisingly, Beaton was for an alliance with Catholic France and ensured the treaty was rejected. That rejection prompted the 'Rough Wooing', and English forces spent the next several years attacking the Scots, which led to Mary being exiled for her safety. The war continued after both Beaton and Henry VIII died and it was then that Henry II of France stepped in with an offer of military assistance in exchange for Mary's hand for this son. A Scottish Parliament agreed to a French marriage treaty on the 7th of July, 1548.
Once the French agreement was formally ratified, Mary, then six, was sent to France, to be raised in the royal court until the pair had reached a decent age to be married. They must've made an odd couple at the wedding; Mary was 5ft. 11in. tall – hence her nickname of 'Lang Mary' – and was fluent in several languages, whereas François was truly wee and had a bit of a stutter.
When Mary, who was fifteen, married the fourteen years old Dauphin at Notre Dame de Paris on the 24th of April, 1558, their union seemed destined to give the throne of Scotland to the future kings of France along with a claim to the throne of England. Mary's claim to England stemmed from her great-grandfather, Henry VII, and the elder sister of Henry VIII, but the Third Succession Act and the last will and testament of Henry VIII meant that Elizabeth was to be heir to her sister, England's Mary I, and the Stewarts were specifically excluded from the English throne. At the time, in the eyes of many Catholics, Elizabeth was illegitimate – because she was the daughter of the opportunistically Protestant Henry VIII and the offspring of an unlawful marriage – and Lang Mary was the rightful heir.
After the marriage ceremony, France's Henry II cheekily proclaimed his eldest son and his new daughter-in-law King and Queen of England. The newly wed royal couple even had their royal arms quartered with those of England. As a consequence, Elizabeth I of England took a dislike to Mary I of Scotland and you might recall how that relationship ended. Her ain folk back in Scotland weren't too happy either when it transpired that a secret clause, signed by Mary on the 4th of April, 1558, amounted to an agreement that, if the royal pairing didn't result in any bairns, Scotland would become part of France and France would inherit Mary's claim to the English crown.
As things turned out, François and Mary had no children. They may well have had, but for a couple of things. For one, François' testicles didn't drop and there is doubt over whether or not the marriage was ever consummated. For two, he died prematurely after just over two years and seven months of married life. Mary was hard on husbands. As Mary's first husband, François wasn't married for long, establishing a trend. François didn't reign for long either, with a mere fifteen months passing before he died on the 5th of December, 1560, from an complications after an ear infection. He had been a sickly child and a fragile teenager – hardly an adult – both physically and psychologically.
As the couple had no issue, François' younger brother became Charles IX, at the age of ten, and his mother, Catherine de Médici, became Regent of France on his behalf. Marie Stuart, Queen of Scots, a widow for the first time, returned to her ain country, where she landed in Leith on the 19th of August, 1561. By the time Mary returned to Scotland, her mother had died (on the 11th of June, 1560), and the Protestant Lords of the Congregation were in control, despite the support of the Scottish Catholic faction and French troops.
The Protestant Lords had been supported by English troops as both they and Elizabeth I had wanted the reformed religion to prevail. The outcome of that bit war was the tripartite Treaty of Edinburgh, signed on the 6th of July, 1560. That treaty sent the French home again and ordained that François and Mary had to stop flaunting the English arms on their heraldry, because France's negotiators had agreed to recognise Elizabeth's right to rule England. Scotland's negotiators hadn't sought Mary's opinion either and so she and wee François refused to ratify the treaty. To make matters worse, just a few weeks afterwards, the Scottish Parliament had established protestantism as the state religion. Mary sure didn't come back to much of a welcome in Scotland.