The former Invercargill man , who now lives south of London, was given exclusive access to photograph the royal family before their 1970 tour to New Zealand, and the photos ended up in and on everything from newspapers to magazines to biscuit tins.
Before the job at the royal family's Sandringham property, the now 81-year-old worked at the NZ Herald in Auckland and then moved to Sydney.
He and a journalist colleague then decided to take the slow route to England, putting their vehicle on a boat in Perth to Singapore and driving to England.
About six years later, in December 1969, he was working for the Daily Mirror and the royal family were readying themselves for their New Zealand tour.
Queen Elizabeth decided she wanted a Kiwi photographer to take the commemorative photos of the family for the tour and Rowntree was contacted.
After arriving and setting up his equipment, he felt himself being pelted with objects.
"While I was arriving and starting to get things set up I was attacked by Prince Edward firing his Christmas present at me which was a ping pong gun.
"I turned around and there is a very smiling 5-year-old lad with his Christmas present."
Any chance of a photo though was quickly dashed by the royal courtier.
"The [courtier] looked at me and he said, 'Bill if you take a picture of the prince firing ping pong balls at you, the Daily Mirror will be barred from royal functions for life'.
Rowntree, who worked for the Daily Mirror for 36 years before retiring in 2001, then met the rest of Edward's family, including Queen Elizabeth and Prince Philip, who died late on Friday night (NZ time), who he was pleasantly surprised to find were "very friendly and helpful".
"What impressed me was just how friendly they were even though it was a semi-formal occasion.
"I was 30 and had been in England six years and this was my first contact with royalty."
While he wasn't sure what their itinerary was at that stage, he got the impression the royals were keen to meet "an ordinary New Zealander talking about his own country".
He proffered his own life and working history in New Zealand as his 10 month-long drive across the world, which they were fascinated in, he said.
The photo shoot went well enough for Prince Philip to ask Rowntree to join him and the Queen for a sherry later that evening.
Given the urgency of processing the photos, it was an offer he was unable to take up.
"Unfortunately we couldn't because I had to get the film all back to London. That would have been incredible.
"I said 'I'm really really sorry but I've got a photo lab waiting to process all the film and get it all sorted, but thank you very much.
"It was a fascinating experience."
The photos from the shoot were eventually released by the royals about two weeks before the tour and used for all sorts of promotions and associated nik naks including the biscuit tin which remains in his kitchen, full of biscuits, to this day.
The tour itself, to celebrate the James Cook bicentenary, notched up several firsts: Charles and Anne's first visit to New Zealand; and in Wellington, the Queen first tried the "walkabout", where she got out of her vehicle about 50m before her destination and mingled with the public.
It continued from that day.
While visiting family in New Zealand in 1971, Rowntree was given the commemorative biscuit tin by his mother.
He often joked to friends how he was the only photographer he knew to get their own photo on a biscuit tin.
"I think I have always joked, I don't think a lot of other photographers have ever been published on a biscuit tin lid before, and I think that's what amuses me most of all.
"The biscuit tin is a little more lasting and still in use. It lives in our kitchen full of biscuits."
