A More Personal Union

In 1560, Francis II was the King of France. His wife, Mary Stuart, was Queen of Scotland. It looked like France and Scotland were settling down into a formal Personal Union--when Francis died under a year into his reign of an infection brought on by a cold. And so, Mary went back to Scotland, and history as we know it happened.

But what if Francis had survived--at least a bit longer? Long enough to produce an heir?

Well, perhaps this.

An alternate timeline on AlternateHistory.com, A More Personal Union details what Francis' longer reign entails. Needless to say, it's interesting for France...

Historical characters who appear or are referenced in the timeline:

Francis II, King of France: The eldest son of Henry II and Catherine de Medici. Sickly, weak-willed, and easily-led... mostly.
Mary, Queen of Scots: Also Queen Consort and later, Queen Mother of France. Has one child with Francis, a son named Henry after the King's father. Henry is nicknamed "le Cyclope" because he is blind in one eye.
Elizabeth, Queen of England: Once Francis and Mary have a son - who has a very strong claim to the English throne - and it becomes clear that the personal union between France and Scotland will endure, she entertains the idea of getting married and bearing her own heirs more seriously than in our timeline. She decides against it, and comes to accept Henry as her Heir.

Tropes used in A More Personal Union include:

Alternate History
Aristocrats Are Evil: While obviously there's something of a mix, the House of Guise seem to be living this trope.
Arranged Marriage: One that's happened before the story begins can be said to kick things off, and many more occur as the story goes on.
Big Little Brother: Henry Valois is this to Charles.
Cheese-Eating Surrender Monkeys: Subverted to hell and back. France doesn't surrender. Not even when facing excommunication, civil upheaval and Spanish invasion. At the same time.
The Chessmaster: Francis' mother, Catherine de Medici.
A Child Shall Lead Them: Happens first with young Francis, and then again with his son, Henry III.
Deadly Decadent Court: The French Royal Court, to a T.
Eyepatch of Power: Henry III starts wearing one after assuming his throne, embroidered by his wife with the French lily, Scottish thistle and English rose.
Fisher King: Francis II verges on this at times.
God Save Us From the Queen: Catherine, the Queen Dowager of France and Mary, the Queen Consort (and other Queen Dowager) of France spend the entirety of their regency locked in a rivalry, jockeying for power. The state of the country is secondary in this contest.
- Averted by Madeleine, Queen Consort of France and Henry III's wife. She is a Shrinking Violet who would much rather not be involved with politics.
Gossipy Hens: The French Royal Court, once again.
The Heretic: Quite a few of them, including Francis II, if you agree with the Pope.
Ill Boy: Francis II is... not in the best of health.
My Girl Is Not a Slut: Francis II's reaction to rumours that his wife has cuckolded him.
Obnoxious In-Laws: Mary and Catherine de Medici don't get along. At all.
One Steve Limit: Averted, as is typical among royal and aristocratic families. Lampshaded In-Universe, with Henry III, King of Navarre (who also became Henry IV, King of France in our history), becoming known as "Henri l'Autre", or the other Henry, because of an already reigning Henry III who is King of France.
The Pope: Plays a bit of a role.
Regent for Life: What Catherine was for Francis II. Catherine and Mary were also engaged in a power struggle about who would get to be this to Henry III. Henry defies this by staging a coup and throwing them both out of the court.
Rousing Speech: These are quite common. Most notably, Francis II's speech at Notre Dame where he founds the Gallican Church.
Sibling Rivalry: Charles and Henry Valois have a certain level of this.
She Is the King: King Augusta of Poland.
Smug Snake: Philip II of Spain, who plots against Francis quite frequently.
Start My Own: Francis II decides to pull a Henry VIII and separates the Gallican Church from Rome.
Teen Genius: Henry III is only 13 years old when he stages a coup to take back his throne from his mother and grandmother.
Ugly Guy, Hot Wife: Francis II and Mary, Queen of Scots.
Unwitting Pawn: Cardinal Charles de Lorraine is quite frequently played by Catherine de Medici.
Violent Glaswegian: Scotland's politics are... interesting.
War Is Hell: The war between Spain and France heads into this direction, leaving both major participants badly off.