The recent abdication of Pope Benedict and the Netherlands' Queen Beatrix have fuelled speculation in Britain Queen Elizabeth may also end her 61-year reign.
The monarch, 87, has been avoiding long flights and her son, Prince Charles, and grandson, Prince William, have toured on her behalf.
For the first time the Queen will not be at the Commonwealth heads of government summit in Sri Lanka this year.
There has been speculation that the Queen might call it a day.
This week the Belfast Telegraph wrote: "It is possible to continue like this, gradually fading away until some medical crisis intervenes, but it would be a downhill path.
It would be far better to quit while she still has some time to enjoy with her husband and family in the honoured role of mother, or grandmother, to the king."
Royal watchers say it is unlikely the Queen will step aside, and say on her 21st birthday, she stated: "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."
Britain's longest serving monarch was Queen Victoria, whose reign was 63 years, 7 months and 2 days.