Wednesday is a big day for the British Monarchy, as this is when Queen Elizabeth II becomes the longest-reigning monarch in British history, having acceded to the throne on February 6 1952, aged 25.
Around 5.30 p.m. London time (12.30 p.m. ET), the Queen will surpass the previous record held by Queen Victoria (1837 to 1901), who ruled for 63 years and 216 days.
CNBC takes a look at some of history's other longest reigns.
– By CNBC's Alexandra Gibbs.
Queen Elizabeth II has established herself as a global brand thanks to her extensive array of royal appearances and her strong relationship with the public.
During her reign, she has taken the role of head of the Commonwealth countries (former British colonies), attended numerous events both formal and informal and transformed how the British monarchy is structured.
For instance, she has ended the rule of male-preference primogeniture – meaning either gender can take the throne, not just the oldest son.
King Sobhuza II of Swaziland in southern Africa is the longest-reigning sovereign to date, holding the throne for 82 years. He came to power only a few months after he was born and maintained his position until his death in August 1982.
Sobhuza's grandmother acted as regent before handing him full control of the throne in December 1921, according to the Swaziland National Trust Commission.
During his reign, one of Sobhuza II's biggest achievements was peacefully gaining national independence from Britain in September 1968.
He was succeeded by Swaziland's current king, King Mswati III.
At four years of age, Louis XIV became King of France after his father died. Louis XIV assumed full control at age 18, after his father's chief minister, Cardinal Mazarin – who acted as regent along with Louis XIV's mother – died.
During his reign, Louis XIV was identified as the "Sun King" – a source of light for his society – and was known for his interest in religion. He held the throne until he died of gangrene in 1715.
Louisa XIV's successor, Louis XV, who took the throne in 1715, was another long-timer, reigning for around 59 years.
Thailand's Bhumibol Adulyadej is the world's longest currently reigning monarch. He took the throne on June 9, 1946, after his brother, then king, was killed in a shooting. This forced Adulyadej to halt his studies temporarily to return to Thailand.
Adulyadej has reigned for 69 years so far, mantaining his position despite several military coups. He remains an influential leader, despite multiple health problems.
Dom Pedro II – known as the "magnanimous" ruler – reigned Brazil for more than 58 years as emperor from the age of five.
During his reign, Brazil enjoyed technological advances such as its first telephone and the economy thrived.
Brazil became a Republic after Pedro II was overthrown and went into exile with his family. He acknowledged the change as a "natural evolution," according to The Library of Congress.
In late 1926, Hirohito became Emperor Showa of Japan after his father died.
Hirohito reigned for over 62 years as a "symbol of the State," providing stability and working with foreign ambassadors and heads of states. He studied marine biology after World War II.
His son, Akihito, ascended the throne after his father passed in January 1989 and currently acts as Japan's 125th emperor.
Before 1911, China was ruled by a number of dynasties, the last of which was the Qing dynasty. One of the most significant emperors from the Qing dynasty, Kangxi Emperor, took his position in the early 1660s (1661/1662), and ruled for around 60 years.
Kangxi was dedicated to stabilizing the Chinese empire, while promoting art and culture. His grandson, Qianlong Emperor, was another long-term monarch, reigning for nearly 60 years (1736–1795/1796).
Ivan IV Vasilyevich may have been pigeonholed as "Ivan the Terrible" by historians, but he did manage one of the longest reigns in the history of Russia's monarchy.
Born in August 1530, it was only three years later that Ivan IV was crowned "Grand Prince of Moscow", after his father wished for it on his deathbed. However, it wasn't until 1547, that Ivan IV was formerly crowned as Tsar of Russia.
Ivan IV was known for his "terribleness" because of his "bloodthirsty habits and cruel personality" along with his desire for territorial expansion.
Tsar Nicholas II was the last Tsar and Romanov to rule in Russia. After he and his family were executed in 1918 at the height of the Russian Revolution, the Russian monarchy ceased to exist.
At the age of 10, Wilhelmina, Princess of Orange-Nassau, became Queen of The Netherlands after her father, King William III, died. Her mother, Queen Emma, acted as her regent until 1898.
During her reign, Wilhelmina was renowned for her strong opinions and outgoing nature, however, she acted as an icon for neutrality during World War I.
Wilhelmina fled for London in 1940, after Germany invaded the Netherlands during World War II. After the war, her public popularity deteriorated and in 1948, she abdicated and was succeeded by Queen Juliana.