Joe Little, of Majesty magazine, said Elizabeth II, who has died after more than 70 years on the throne, has left the institution on a “very sound footing”.
She was strong in character but a reserved Queen who kept her innermost thoughts to herself, Mr Little said.
He described the Queen’s many decades on the throne as a “massive achievement”.
Mr Little told the PA news agency: “The fact that the British monarchy has survived in the way it has, and seemingly is on very sound footing despite occasional glitches, is testament to the steadfastness of Queen Elizabeth II.”
He added: “I think we would all like to think we knew a lot about the Queen, but did we really?
“Despite her status and longevity as head of state, she was a reserved character throughout her life and had to overcome that, but we didn’t know her innermost thoughts.”
High points during her reign included her jubilees, her state visits and tours around the globe.
Her historic visit to Ireland in 2011 was a favourite of the Queen’s, Mr Little said.
She was the first British monarch to travel to the Republic since the nation gained independence from Britain, and the trip was hailed as a new era in relations between the two countries, despite the past Troubles.
Mr Little said: “The state visit to Ireland was one of her personal high points, given it was something she had wanted to do for such a long time.”
But her annus horribilis of 1992 was an undeniable low point.
“Who would have predicted that so many horrible things would happen at the same time – the children’s marriages unravelling and then the fire at Windsor Castle on her 45th wedding anniversary, so that took a lot of getting over but she was of a strong character,” he added.
Mr Little said the Queen’s pledges to serve for her entire life earned her great respect throughout the country.
“There was huge admiration – her devotion to duty, the fact that she was still working in her 90s at a time when many of her subjects would have been retired for 30 years.
“The oath she took at the time of her coronation and the speech she gave for her 21st birthday, she took incredibly seriously and never was there an intention to quit as old age took its hold.”