In 1688, the Parliament of England overthrew its second king: ousting the Catholic James II, it invited in his daughter and son-in-law to take the throne as Mary II and William III. Not long thereafter, it instituted new laws to ensure that no Catholic could ever take the throne. The trigger for all this was the birth of a son, James, to the king, who supplanted his sisters in the line of succession.
Let's imagine a different Glorious Revolution: rather than straight up kicking out the king, Parliament bullied him into changing the law of succession. Now, the eldest child of the monarch would take the throne, male or female. Prince James was no longer Crown Prince, but sat third in line to the throne.
-1. Charles I
b. 1600, r. 1625-1649
== Henrietta Maria
0. Charles II
b. 1630, r. 1660-1685
Mary
1631-1660
== William II of Orange
William III of Orange
1650-1702
1. James II
b. 1633, r. 1685-1701
== (1) Anne Hyde
== (2) Mary of Modena
Mary
1662-1694
2. Anne
b. 1665, r. 1701-1714
== George of Denmark
3. James III
b. 1688, r. 1714-1766
== Maria Clementina Sobieska
4. Charles III
b. 1720, r. 1766-1788
5. Henry IX
b. 1725, r. 1788-1807
Henrietta
1644-1670
== Philippe of Orleans
Marie Louise
1662-1689
Anne Marie
1669-1728
== Victor Amadeus
Marie Adelaide
1685-1712
== Louis
Louis XV of France
1710-1774
== Marie Leczinska
Louise Elisabeth
1727-1759
== Philip of Parma
Isabella
1741-1763
== Joseph II of Austria
Maria Theresa
1762-1770
Ferdinand
1751-1802
== Maria Amalia
Carolina
1770-1804
== Maximilian of Saxony
6. Amalie
b. 1794, r. 1807-1870
== Franciscus de Merendonque
Johannes
b. 1817. Son of a secret
marriage; not held to be
in the line of succession.