Final answer:
In 2016, Elizabeth II became the world's longest-reigning living monarch when the king of Thailand died after a 70-year reign.
Step-by-step explanation:
In 2016, Elizabeth II became the world's longest-reigning living monarch when the king of Thailand died after a 70-year reign. This significant event solidified Elizabeth II's position as the monarch with the longest reign in modern history. It is a testament to her enduring presence and dedication to her role as the Queen of the United Kingdom and other Commonwealth realms.