Queen Elizabeth II, at 90 years of age, has been battling a “heavy cold” and staying out of the public eye during her family's annual traditions over the holidays, sending people into a frenzy of concern and curiosity about who may take her place should she die or step down from the throne. Should either scenario play out, there’s one thing for sure: It would be the end of the longest serving current monarch in the world.

The queen became the monarch at the age of 25 when her father, King George VI, died sometime in the night of Feb. 5, 1952. She has served ever since, a span of nearly 65 years that has given her a range of experiences over the years including the opportunity to meet 12 of the past 13 American presidents.

The next longest-serving monarch, the Sultan of Brunei, Hassanal Bolkiah, has been on the throne for 49 years.

Elizabeth wasn’t even aware of the change in her royal status the day that she became queen 64 years ago.  Her father died in the middle of the night while she was on a trip to Kenya to watch elephants gathering at a watering hole before she was scheduled to continue on to make stops in Australia and New Zealand. It wasn’t until late the next day when Elizabeth was told about the death.

Her formal coronation event to become the queen of the United Kingdom, Canada, Australia, New Zealand,  South Africa and Ceylon was held June 2, 1953.

She’s met plenty of world leaders in addition to the 12 U.S. presidents who have been in office during her time as queen (she met one of the above mentioned 13 presidents while she was a princess and did not meet Lyndon B. Johnson). During her reign, she has seen seven Roman Catholic popes inhabit the Vatican as queen and has visited that holy place three times. She’s traveled overseas more than 250 times and touched down in more than 115 countries.