Elizabeth II
During her grandfather's reign, Elizabeth was third in the line of succession to the throne, behind her uncle Edward, Prince of Wales, and her father, the Duke of York. Although her birth generated public interest, she was not expected to become queen, as the Prince of Wales was still young, and many assumed that he would marry and have children of his own. When her grandfather died in 1936 and her uncle succeeded as Edward VIII, she became second-in-line to the throne, after her father. Later that year Edward abdicated, after his proposed marriage to divorced socialite Wallis Simpson provoked a constitutional crisis. Consequently, Elizabeth's father became king, and she became heir presumptive. If her parents had had a later son, she would have lost her position as first-in-line, as her brother would have been heir apparent and above her in the line of succession.

Q: What did Edward's proposed marriage to Simpson cause?
constitutional crisis