Queen Elizabeth II was set on Thursday to become Britain's oldest monarch, overtaking her great-great grandmother Queen Victoria amid signs the royal family is preparing for life after 81-year-old "Lillibet".
Victoria died in 1901 aged 81 years and 243 days, and Elizabeth will mark passing the milestone with neither pomp nor ceremony, spending the day as usual with her husband of 60 years, Prince Philip.
According to Buckingham Palace, Elizabeth was to pass Victoria's record at around 5:00 pm (1700 GMT) Thursday -- taking into account times of birth and death. Other observers, counting only in whole days, put the mark as Saturday.
She is the world's second-longest living monarch, after Thai King Bhumibol Adulyadej; has outlasted 11 prime ministers -- the first was Sir Winston Churchill -- and is the first to have a premier, Tony Blair, born in her reign.
Victoria will retain the record for longest-serving monarch ever for some time, though -- she ruled Britain and its empire for nearly 64 years which Elizabeth will surpass if she is still on the throne on September 9, 2015.
Despite her age, the queen shows little sign of slowing down -- last month, she and Prince Philip visited Uganda for the Commonwealth Heads of Government meeting and she carried out 425 official engagements last year.
"Even allowing for the improvement in medicine since Victoria, it is remarkable," Peter Hennessy, professor of contemporary British history at Queen Mary's college, University of London, told the Daily Telegraph.
"I cannot think of any other head of an institution who has not put a foot wrong over such a long period of time.
"In those years, she has presided over the most dignified withdrawal from the superpower status, which is no bad legacy.
"The way she has adapted, without succumbing to faddish fashions, is a gift of genius."
Notwithstanding her gruelling timetable and the high respect which most Britons have for her, there are signs that the monarchy is starting to think about what will happen when she dies, even if she is in good health.
Heir to the throne Prince Charles went to Uganda last month with his parents, attending the Commonwealth summit for the first time.
The queen is head of the Commonwealth, made up of 53 mostly former British colonies, but the right of her successor to take over from her is not automatic -- instead, the organisation's leaders must decide.
The Daily Telegraph newspaper quoted an unnamed senior Commonwealth source at the time saying the question of whether Charles will become head of the body is being actively considered.
Charles's own position in Britain has become stronger thanks to the successful integration of his second wife Camilla -- with whom he had an affair during his marriage to the late princess Diana -- into the royal family.
Thanks to her low-key charity work and seemingly warm relations with stepsons Princes William and Harry, public opinion of the woman Diana dubbed "the Rottweiler" is beginning to thaw.
Some 28 per cent of people say they want her as queen when Charles takes over, compared to just seven per cent in 2005.
Insiders including Elizabeth's cousin Margaret Rhodes say it is highly unlikely she will step down early -- the abdication of Edward VIII in 1936, which forced her father to take over, is a painful chapter in royal history.
"Abdication I don't think is an issue, or something that's even in consideration to the Queen," said Robert Jobson, a journalist and author of books on the royal family.
"As long as she remains in good health, she will continue to be queen until the day she dies. Otherwise the system does not really work," he told AFP.
So while the queen could still, in the words of the national anthem, be "long to reign over us", the royal family seems determined to make sure that, when the inevitable does finally happen, the transition is smooth.