Tayoubi said the researchers were "very surprised" after the first imaging results came in when they noticed a "very big anomaly", which turned out to be the void.
Analysis also shows the void connects with the burial chamber of the pharaoh Khufu whose remains inhabit this giant memorial site.
What lies in the middle of the structure has been subject to debate for years as researchers were unable to get a look inside.
A team of archaeologists discovered this week a hidden chamber in Egypt's Great Pyramid of Giza.
In a report in the journal Nature, researchers from the "ScanPyramids" team used a method of tracking cosmic particles to scan the inside of the pyramid. Muons are by-products of cosmic rays and are only partially absorbed by stone.
The exact shape and size of the void is fuzzy - its objective and possible contents a mystery.
There were three known chambers inside the Great Pyramid-an unfinished low chamber near the bedrock, as well as the king and queen's chambers, believed to be for Pharaoh Khufu and his wives-until today.
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The Verge laid out a succinct, easy to understand, and extremely radical-sounding explanation of muons: "Muons are produced when the cosmic rays that permeate our Universe and pummel our atmosphere break down - creating a kind of subatomic confetti that rains down on Earth at nearly the speed of light".
"We don't know whether this big void is horizontal or inclined; we don't know if this void is made by one structure or several successive structures", explained Mehdi Tayoubi from the HIP Institute, Paris.
"In order to construct the Grand Gallery, you had to have a hollow, or a big void in order to access it - you can not build it without such a space", he said.
The scattering of the muons was recorded on an extremely sensitive photographic medium known as nuclear emulsion film, which had been positioned in the Queen's chamber, inside the pyramid. However, some historians are more excited than others about the discovery.
Keep scrolling to see how the scientists found the void as well as the technology they used.
Mark Lehner and Zahi Hawass, members of the Egyptian Ministry of Antiquiteis' scientific committee - both of whom saw the findings - told The Atlantic they suspect it is a "construction gap".
Hany Helal of Cairo University, coordinator of the ScanPyramids project, put the open question to the academic community: "We open the question to Egyptologists and archaeologists: what could it be?"