Dawn Brook, this year now 69
When Dawn Brooke became the world's oldest natural mother at 59 it left doctors with a mystery to solve.
How was it possible for the British housewife, who was well beyond the average age for the menopause of 51 and was not having any fertility treatment, to produce the egg that allowed her to conceive?
Now the Daily Mail can reveal that Mrs Brooke, who gave birth to a healthy son, Harry, was on hormone replacement therapy when she conceived.
This, the experts believe, may have led to the astonishing pregnancy and birth in 1997 - which the family kept secret for a decade.
HRT is normally taken after a woman has gone through the menopause and is unable to conceive.
However, fertility doctors believe in rare cases it is possible that the hormones in the medication can cause the ovaries to release a few last eggs.
There have been a number of previous cases of women, who had already gone through an early menopause, falling pregnant while on HRT.
A family friend said: "She had upped her dose before a romantic weekend away when she thinks she became pregnant with Harry.
"She wasn't on any fertility treatment or IVF but she was on HRT at the time and they think it might have been the thing that caused the pregnancy."
The world's oldest mum, Dawn Brooke, in 1980
Dr Geeta Nargund, head of reproductive medicine at St George's Hospital, London, said: "There are rare cases of spontaneous ovulation for women on HRT.
"In the past we've seen it happen with women who have gone through early
menopause. There's a very small chance of that happening.
"It's possible for ovulation to continue on and off around the age of menopause but not once a woman is completely postmenopausal."
Mrs Brooke married Harry's father, Raymond Brooke, now 74, at their £1million home in Guernsey in the summer of 1997.
A few weeks later she gave birth by caesarean at the island's Princess Elizabeth Hospital.
Mrs Brooke was desperate to keep her record a secret.
A friend said: "She was completely shocked when she realised that she was the world's oldest natural mother and didn't want anyone knowing about it.
"She looks very young for her age and so most people were probably unaware that she was 59 when she gave birth."
Even the couple's close friends did not know.
John Trowbridge and his wife, Jean, who are Harry's godparents and who were also witnesses at the Brookes' wedding, were not told.
Mr Trowbridge said: "We never knew Dawn's age and they never mentioned anything about her being the world's oldest natural mother to us. It's a big surprise."
Details of the record finally emerged last month when the family spoke of their happiness at
having a son so late in life.
They told how Harry was an exceptionally bright boy who excels at maths.
Like many 10-year-olds, he is also a fan of Harry Potter.
London-born Mrs Brooke has a daughter, Lisa Loftus-Otway, 39, who lives in Austin, Texas, and son Nick Otway, 33, from a previous marriage.
Her mother, Gladys Chivers, lives in a nursing home in Sussex and turns 101 next week.
Mr Brooke was born in Yorkshire and worked in computers in California for 25-years before settling in the Channel Islands.
He has two adult daughters from his first marriage. They live in the U.S.
Doctors say it is extremely rare for a woman to have children once past their mid 50s - and it is very unusual for a woman over 54 to be ovulating.
The world record for the oldest non-IVF births was held by Ruth Kistler who, at 57, had a daughter in Los Angeles in 1956.
The British record for the oldest birth without fertility treatment was set by Kathleen Campbell of Kimberley, Nottinghamshire.
She was 55 when her son Joby was born in 1987.
The world's oldest mother is Carmela Bousada who gave birth last December, seven days before her 67th birthday, after she lied to doctors about her age to undergo IVF treatment.
Patricia Rashbrook, 62, became Britain's oldest mother last July when she gave birth to a boy conceived through IVF.