At least, that's what researchers at Australia's ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) believe.
Based on data collected by the Hubble Space Telescope, the team calculated that the detonation occurred a little more than 3 million years ago.
The energy flare - or Seyfert flare as it's known - started near the that's in the centre of our galaxy.
So powerful was the blast, according to ASTRO 3D, that it shook the Magellanic System-a trail of gas extending from the nearby Large and Small Magellanic Clouds-some 200,000 light years away.
One scientist on the study, Professor Bland-Hawthorn, noted that the flare would have been like darkness and then someone switching on a lighthouse beacon for a brief period.
"It's an fantastic thought that, when cave people walked the Earth, if they'd looked off in the direction of the galactic center, they'd have seen some kind of giant ball of heated gas", Bland-Hawthorn said in a video accompanying the study. For example, the asteroid that wiped out the dinosaurs struck Earth 60 million years before this explosion, which occurred when our ancient Australopithecine ancestors were already wandering in Africa.
"This is a dramatic event that happened a few million years ago in the Milky Way's history", says Professor Lisa Kewley, Director of ASTRO 3D.
"This shows that the center of the Milky Way is a much more dynamic place than we had previously thought", she continued.
We're lucky, mostly. The huge flare seems to have exploded "up and down" from the galactic plane, rather than across the galaxy.
It's estimated to have lasted for around 300,000 years, which is extremely short in galactic terms.
In conducting the research, Professor Bland-Hawthorn was joined by colleagues from the Australia National University and University of Sydney, and, in the U.S., the University of North Carolina, University of Colorado and the Space Telescope Science Institute in Baltimore.
"These results dramatically change our understanding of the Milky Way", says co-author Magda Guglielmo from the University of Sydney. The black hole is known as Sagittarius A*, or Sgr A, * and has a mass 4 million times that of the Sun.
In 2013, Bland-Hawthorn and colleagues published the first evidence of this eruption in The Astrophysical Journal. This recent flare opens the possibility of a complete reinterpretation of its evolution and nature. However, even though it is considered the prime suspect, the researchers note that more work still needs to be done.
An enormous energy flare ripped through our galaxy 3.5 million years ago, a team of scientists has discovered. "We are the witness to the awakening of the sleeping beauty". That doesn't make us completely safe from the monster black hole that resides at the galaxy's core.