It was the first time a researcher had made a direct correlation between the stars and the locations of the Mayan cities, the Journal de Montreal reported.
But William pressed on with his research, eventually coming to realise that there was one star in another constellation that didn't appear to have a corresponding city.
If his theory and calculations were correct, that would place the missing city in a remote coastal location on the Yucatán Peninsula in Mexico.
Using satellite images from the Canadian Space Agency and Google Earth maps, William zeroed in on the precise location - and a pyramid and about thirty ancient buildings were spotted, partially hidden, in the dense forest.
"There are linear features that would suggest there is something underneath that big canopy,"
Canadian Space Agency liaison officer Daniel de Lisle told The Independent.
"There are enough items to suggest it could be a man-made structure."
William has named the lost city K'aak Chi, or Mouth of Fire. It is believed to be one of the five largest Mayan cities on record.
The discovery has won William praise from space agencies in Canada and Japan as well as NASA. He's also become a local hero in Quebec.
"What makes William's project fascinating is the depth of his research," Mr de Lisle said.
"Linking the positions of stars to the location of a lost city along with the use of satellite images on a tiny territory to identify the remains buried under dense vegetation is quite exceptional."
The young scientist - whose passion for the ancient civilisation was sparked by reading Mayan doomsday prophesies in 2012 - was thrilled with his remarkable breakthrough.
"I did not understand why the Maya built their cities away from rivers, on marginal lands and in the mountains," he told the Journal de Montreal.
"They had to have another reason, and as they worshipped the stars, the idea came to me to verify my hypothesis.
"I was really surprised and excited when I realised that the most brilliant stars of the constellations matched the largest Maya cities."
The jungle that houses the newly discovered city has not been explored, but William said he couldn't wait to see it for himself.
"It would be the culmination of my three years of work and the dream of my life," he said.