Charles II, Elector Palatine (
https://en.wikipedia.org/wiki/Charles_II,_Elector_Palatine) was the cousin of OTL George I of Great Britain, and (please correct me if I'm wrong) would have been the heir to Queen Anne Stuart instead of his Aunt, Sophia of Hanover.
IOTL, he died childless in 1685 at the age of 34. What if he had survived and he, or a son, lived long enough to succeed Anne? By Anne's death in 1714, Charles would have been 63 years old, as opposed to George who was 54 and who passed away at the age of 67. Another consequence of his death was that the Electorate of the Palatinate passed to his Catholic cousin, Philip William of Neuburg.
EDIT: Charles was married to Princess Wilhelmina Ernestine of Denmark, but the marriage was unhappy and Charles' father was considering divorcing the two before his death. I imagine, if not for his death, the younger Charles would have divorced her and married someone else. Three candidates I found were:
Elisabeth of Mecklenburg-Güstrow (
https://en.wikipedia.org/wiki/Elisabeth_of_Mecklenburg-Güstrow)
Fredericka Elisabeth of Saxe-Eisenach (
https://en.wikipedia.org/wiki/Fredericka_Elisabeth_of_Saxe-Eisenach)
Anna Sophie of Saxe-Gotha-Altenburg (
https://en.wikipedia.org/wiki/Anna_Sophie_of_Saxe-Gotha-Altenburg)