This week, Prince William, the grandson of Queen Elizabeth II, had a son. That means the new baby is third in line to the British throne; but it could be decades before his reign starts.

According to the Economist, Prince Charles, 64 and first in line, will soon become the longest king-in-waiting.

Since the first William (the Conqueror), the average age of accession has been 3, which coincidentally is Prince William's current age).