As the African country celebrates the end of the 93-year-olds reign, that spanned over three decades, the Queen takes on the new title as she continues her 65 years on the throne.
Elizabeth surpassed her great-great-grandmother, Queen Victoria, as the longest-reigning monarch back in 2015.
In the list of oldest head of state’s, the Queen is followed closely by Beji Caid Essebsi, president of Tunisia.
The 90-year-old was the first to win an election after the Tunisian revolution following the Arab Spring.
Emperor Akihito of Japan turns 84 next month but seems set to retire his position with speculation that the country’s Imperial Household Council have discussed two dates in mind for the emperor to abdicate.
Rumours were fuelled further after a top government spokesman announced earlier today that a date was being discussed for Akihito to stand down.
They said: "After hearing the panel\'s opinion, based on that, we would like to decide the date promptly.”
The Queen and Prince Philip celebrated their 70th wedding anniversary on Monday with the couple captured in a new portrait taken to mark the occasion.
The stunning photos offer an insight into the everlasting love of Britain’s head of state and her husband, the Duke of Edinburgh, as they prepare to mark the milestone, making them the longest married couple in British royal history.
And the sequence of images, taken by British photographer Matt Holyoak, of Camera Press, prove the Queen and her Greek prince, still today, only have eyes for each other.
The longest-reigning monarch looks elegant in a cream day dress by Angela Kelly, the same frock she wore at the Diamond Wedding Anniversary Service of Thanksgiving.
In a poignant effort to mark seven decades of marriage with her childhood sweetheart, the Queen also shows off her \'Scarab\' brooch in yellow gold, carved ruby and diamond, designed by Andrew Grima, which was given to her by her husband in 1966.
In one stunning picture, Queen Elizabeth II gracefully sits on an elaborate gold-rimmed chair as her sprightly 96-year-old husband stands beside her with his hand in his pocket photographed against a platinum-textured back drop.
The picture is perhaps a nod to the fact the Duke dedicated his life to be by the side of his wife through thick and thin.
The Queen and Prince Philip celebrated their 70th wedding anniversary on Monday
Emperor Akihito of Japan turns 84 next month but seems set to retire his position
The Duke of Edinburgh vowed to act as the Queen’s “eyes and ears” when he married the soon-to-be-monarch 70 years ago on November 20, 1947.
And after more than 65 years by the Queen\'s side, Prince Philip certainly made his mark, only retiring at the grand old age of 96 this year.
The couple opted for a low-key dinner party with their close friends and family to celebrate their anniversary at Windsor Castle.