He has been able to date the oak panel painting to 1525, using specialised scanning technology and his own expertise in annual tree-rings.

The portrait had been a source of mystery for the Art Gallery of NSW, which approached Dr Brookhouse, a lecturer at the Australian National University Fenner School of Environment and Society, to help date the work.

Dr Brookhouse had initially examined the work several years ago using standard methods, but was unable to date it without sanding the edge of the panel or otherwise altering the work.

But the gallery more recently had the chance to use a high-tech scanning procedure at the Australian Synchrotron in Melbourne to analyse layer of paint, which co-incidentally revealed the underlying structure of the wood for the first time.

“One of the images had the appearance of wood grain and it was so clear, I could see the tree-rings in the oak,” Dr Brookhouse said.

“I was immediately excited because I knew there was a good chance I could work out the date the tree was felled.”

He said dendrochronology, the science of dating climatic events using annual growth rings in timber, is not widely known in Australia due to the nature of our trees and climate.

“There are very few dendrochronologists in Australia and the gallery thought they’d have to find someone in Europe,” he said.

“To confirm the date, we collaborated with the University of St Andrews in Scotland and University College London to compare our scan with the UK’s tree-ring chronologies.”

He was able to determine the time in which the painting was probably created in the years after the tree was felled, as well as the area in which the tree likely grew, all without having to alter or damage the work.

He said he had a long-standing interest in art, and had first become interested in his own field of research when he heard how European researchers had managed to date Rembrandt paintings.

“My family's background is Dutch, and so that overlap between Rembrandt as a Dutch master and trees and tree rings really prompted my interest in tree rings. So from there going forward, I worked with eucalypt tree rings in particular, to understand climate and forest dynamics,” he said.

And, decades down the track, his diverse interests came full circle when he had the chance to examine the 500-year-old Henry VIII portrait.

“I have to admit that the artistic component of the work didn't strike me as much as the timber,” he said.

“When you work with tree ring materials, you can't help but have a sense of time in the material that you hold in your hand.

“And when that sense of the age of the material is wrapped up in the age of the cultural material as well, that sense of time for me is something that's quite prominent.”

Painting conservator at the Art Gallery of NSW Simon Ives said little was known about the painting before it was purchased by the gallery.

Dr Brookhouse’s research was able to determine not only the time in which the tree was felled and turned into a panel - around the time Henry VIII, ageing and growing fatter, was plotting the downfall of Anne Boleyn - but also that the tree likely grew near Sussex in south-west England.

The scan was also able to reveal where the painting had been altered around the placement of Henry’s hand.

“We have a clearer idea of the manner in which it's been created and we have some idea of the sort of people who were around at the time who could have been involved,” Mr Ives said.

“You get the sense of time melting away, actually. It really makes your hair stand on end when you get that sort of level of intimacy with the painting through those incredibly precise forensic information from the scientific analysis.”

While the actual artist remains unknown, the gallery believes it can link it to an Anglo-Flemish workshop in London where a group of artisans were working at the time.

The painting is now on display at the Art Gallery of NSW, alongside details of the technical research and conservation treatment, until September 9.