Queen Elizabeth, the world's oldest monarch, turns 90 on Thursday showing no sign she will be retiring from the stage anytime soon.
Her birthday comes months after she surpassed the 23,226 days her great-great-grandmother Queen Victoria spent on the throne to become Britain's longest-reigning monarch.
Since turning 65 in 1991, the nation has speculated about whether she would step aside in favour of her eldest son, Prince Charles. But aides and commentators say there is no prospect of her giving up her job.
"The queen has a phenomenal drive and energy and I think the fact that she still works is what keeps her going," Ingrid Seward, editor in chief of Majesty magazine, told Reuters.
"The queen doesn't want to put her feet up. This is what she wants to do, and this is what she's going to do for as long as she's fit and able to do so."
Born on April 21, 1926 in central London, Elizabeth still hosts state visits, presides over the annual state opening of Parliament and holds a weekly audience with the prime minister.
Though she has cut back on her once-demanding schedule of foreign trips, those close to her say only incapacity would stop her from performing her royal duties. Last year she carried out 341 official engagements.
"As she turns 90, she's a remarkably energetic and guiding force for her family," her grandson Prince William said in a speech in India this week. "She may be my grandmother, but she's also very much the boss."
Although Elizabeth's father died at the relatively young age of 56, her mother, who was known as Queen Elizabeth the Queen Mother, lived until 101 and was still appearing in public almost up until her death in 2002.
Some have suggested that one reason for the queen to hang on is the relative unpopularity of her son Charles, 66, already a record-holder as Britain's longest-serving heir apparent.
"When the queen's reign comes to its natural end, there is likely to be an urgent debate about the role of the royal family in modern Britain - a debate whose outcome is uncertain," royal author Anna Whitelock wrote in the Daily Mail.
"There is no absolute guarantee about the monarchy's long-term survival," Whitelock said.
The queen will celebrate her 90th birthday on Thursday when she will open The Queen's Walkway and undertake a walkabout in Windsor before lighting a beacon. She will spend the rest of the day with family at Windsor ahead of a series of public events in the coming months.
The official birthday celebration in June is marked by the Birthday Parade, also known as Trooping the Colour at Whitehall.
Other events include a National Service of Thanksgiving at St Paul's Cathedral on June 10 followed by a Birthday Parade on Horse Guards Parade on June 11.
On June 12, the Queen will attend the Patron's Lunch, which marks the celebration of patronage of over 600 organisations in the UK and around the Commonwealth and will see The Mall in St James Park transformed for its largest-ever street party.