Queen Elizabeth is now the oldest reigning head of state.

Queen Elizabeth

Queen Elizabeth

The 91-year-old monarch has been handed the new title after Zimbabwe president Robert Mugabe, 93, ended his three-decade reign by stepping down from the role earlier this week.

Queen Elizabeth is now the oldest head of state alive today, though she is closely followed by 90-year-old Beji Caid Essebsi, who is president of Tunisia.

This isn't the only impressive title the Queen can boast either, as back in 2015 she surpassed her great-great-grandmother, Queen Victoria, as the longest-reigning monarch, having now ruled over Great Britain for a whopping 65 years.

And she also takes the crown alongside her husband Prince Philip, 96, when it comes to the longest royal marriage, as on Monday (20.11.17) they celebrated their 70th wedding anniversary.

To commemorate the special occasion, a new portrait of the pair was issued, which sees the couple framed on either side by portraits painted in 1781 of George III and Queen Charlotte, who were married for 57 years - the longest royal marriage until their own.

In the photograph - which was snapped by Matt Holyoak of the Camera Press, which is also celebrating its 70th year - Queen Elizabeth is wearing a a cream day dress by Angela Kelly, accompanied by a gold, ruby and diamond brooch Prince Philip gave her in 1966.

The Duke of Edinburgh, meanwhile, is wearing a tweed jacket and burgundy tie.

The portrait isn't the only thing the couple did to celebrate seven decades together, as the Queen also appointed her spouse as Knight Grand Cross of the Royal Victorian Order.

A tweet from the official Royal Family account stated: "Her Majesty has appointed His Royal Highness The Duke of Edinburgh to be a Knight Grand Cross of the Royal Victorian Order (GCVO).

"Awards in the Royal Victorian Order are made personally by The Queen, for services to the Sovereign."

The honour is believed to have been awarded to the royal as a sign of Queen Elizabeth's thanks for showing her his everlasting support both publicly and privately, over the past seven decades of marriage.