The abdication of the King of Spain will not have any bearing on the Queen, who will stand by her promise to serve as monarch for the rest of her life, a royal historian has predicted.
Hugo Vickers said that unlike King Juan Carlos, who is in poor health and has faced a slump in his popularity, the Queen, who is 88, is "firing on all cylinders".
He said: "The Queen is not likely to abdicate. We know from various biographies that she was pretty irritated when Queen Juliana of the Netherlands - Queen Beatrix's mother - abdicated in the 1980s because monarchs shouldn't abdicate.
"Abdication put her father on the throne so abdication is a pretty unpopular word within the Queen's household."
The King of Spain is the second European monarch to abdicate in just over a year. In April last year, Queen Beatrix of the Netherlands handed the throne to her son Prince Willem-Alexander after 33 years. Her mother Queen Juliana of the Netherlands abdicated in 1980 on her 71st birthday.
Mr Vickers said there were unlikely to be calls for the Queen - who was crowned 61 years ago today - to do the same and she seemed to enjoy the experience of her Diamond Jubilee.
"The Queen will not abdicate because she is a consecrated monarch and she pledged to serve throughout her life. She doesn't have to abdicate - if anything goes wrong, she can have a regency like George III," he said.
"As far as I'm concerned, the Queen is firing on all cylinders.
"The King of Spain looked dreadful at the popes' canonisation and was walking with a stick. There's been a lot of drama in his family. It's not a happy situation.
"Recently he's lost a lot of respect and his health has been poor. But as for the Queen, tomorrow she's got a garden party, then the next day the state opening of Parliament, and then she's got a state visit to France."
He added: "The Queen Mother thrived on it until she was 101."
Mr Vickers said there was a strong three-tier Royal Family with a younger generation behind her.
"The Queen has a royal family to support her. She doesn't have to do long-haul flights if she doesn't want to," he said.
"There is now a three-tier family with the Prince of Wales there to support her and the Duke and Duchess of Cambridge and Prince Harry flying all around the Commonwealth. It's now four-tier if you include Prince George."
On her coronation day in 1953, the Queen made a pledge to the nation in a radio broadcast, saying: "Throughout all my life and with all my heart I shall strive to be worthy of your trust."
Six years earlier, as Princess Elizabeth, she accompanied her parents on a tour of South Africa during which she celebrated her 21st birthday.
In a radio broadcast to the Commonwealth during the trip, she made a poignant promise: "I declare before you all that my whole life, whether it be long or short, shall be devoted to your service and the service of our great imperial family to which we all belong."
A Buckingham Palace spokesman said: "It's a matter for the king and the people of Spain."
Social historian Dr Judith Rowbotham said that Britain, in contrast with Spain, has a "sacerdotal monarchy".
"When the Spanish monarchy was restored it was restored very much with a modern constitutional element. It was devoid of any sacred element," she said.
"The British monarchy is a sacerdotal monarchy - as part of the coronation, the monarch goes through a consecration ritual which is similar to the consecration ritual a priest goes through. You can retire from being an active priest but you're still a priest until you die.
"It would provoke a constitutional crisis if a British monarch were to abdicate. With a Spanish king, there is a coronation but not a consecration."
She added that an abdication by the Queen would be "an abdication of duty".
"You die on the job. People might take on the job of an active monarch in your name. When George III became mad, there was no question of him not being king," Dr Rowbotham said.
Dr Rowbotham, founder of the SOLON academic network, highlighted that the Queen's uncle King Edward VIII abdicated in 1936 before he was crowned.
"There was a panic to get him to abdicate before he was crowned. With the constitutional implications of him being crowned and then abdicating, it couldn't be left. It had to be sorted before the coronation."
Anti-monarchy group Republic called on Spain to allow a democratic decision on their next head of state.
Graham Smith, Republic's chief executive, said: "This is Europe in 2014, not 1714. When heads of state stand down the people have a right to decide who succeeds them.
"A royal succession shows us just how simple this issue is: the people need their voices heard when it comes to choosing a head of state. It's not ok to simply pass a public position down the family line."
He added: "The Spanish royals have been beset with scandals - they cannot be allowed to arrogantly pass the Crown from father to son without a vote by the Spanish people.
"It's the same in Britain as it is in Spain - the head of state is an important position that can't be left to chance. The people have a right to vote."