"Did anyone feel that rumble in Bispham, my windows were shaking?," wondered one startled resident at around 11am.
And she wasn't alone.
Hundreds of people took to Facebook searching for answers after the mystery 'boom' rattled windows and shook their floors.
"Heard it in FY4. Thought a bomb went off," said one resident.
"What was that!? Earthquake?," added another.
So what exactly was it?
A spokesman for BAE Systems said: "We can reassure people that the noise reported in the Lancashire area today was a supersonic boom from one of our Typhoon aircraft, which was undergoing flight testing in an offshore range area.
"As the UK’s sovereign combat air capability provider, we regularly conduct flight testing sorties as part of the Typhoon development programme and our broader role in safeguarding national security.
"We operate in airspace cleared for supersonic testing but apologise for any alarm caused to local residents."
The Typhoon took off from Warton Aerodrome and Flight Radar tracked its route from Preston to the Fylde Coast, where it maneuvered out at sea before returning to the airfield.
You can watch video of the Typhoon taking off from Warton in our media player above. The footage was taken just minutes before its supersonic boom was heard across Lancashire.
The awesome sound of the supersonic boom is caused when the fighter jets reach speeds greater than that of sound (Mach1) which is about 767 mph.
The Eurofighter Typhoons can reach a top speed of around 1,550mph and to the human ear, the sonic boom can cause a sound similar to an explosion or a thunderclap.
The boom was felt across Lancashire, but seems to have been particularly loud and forceful around Blackpool and the Fylde.
Later in the afternoon, four American F15 Eagle strike fighters were spotted flying in formation off the Fylde Coast.
It follows reports of a number of RAF and USAF training exercises around the UK today, including a giant American B-52 bomber seen returning to RAF Fairford in Gloucestershire following a training mission around the Mediterranean Sea.
Prior to the confirmation from BAE Systems, the 'boom' had posed a bit of a mystery, with the British Geological Survey investigating out of concern that it might be seismic activity.
The BGS team said it received 'numerous reports' from concerned residents, mainly in the Lancashire area, but also across Merseyside, Greater Manchester and Cheshire, who reported a 'tremor' sometime around 11am.
It said data from its seismic networks was examined and it soon concluded that the signals recorded pointed to "a possible sonic origin" and not a seismic event.
What did the shock waves of the Typhoon's sonic boom feel like to those on the ground?
One person said, "Was in basement of hotel on North promenade, Blackpool, thought a strong wind had knocked/dragged something heavy or a heavy skip had been dragged in the car park."
Another said: "Absolutely terrifying. Fortunately the kids were outside in the garden otherwise plates might have fallen out of the cupboard onto their precious heads!"
"Low rumble building in intensity for 5-10 seconds followed by a bang that made the house shake," described another. "Felt like a steam roller had rolled up to and crashed into the house."
Another Blackpool resident said, "I was in my first floor flat. Thought it was a large waggon passing by but my daughter who I was on the phone to felt and heard it too.
"She is a half hour walk from me. Both heard a loud rumbling and vibration."
"Slight rumbling similar to someone moving heavy furniture around in a neighboring office. Rumbling came in two short bursts within split seconds of each other," said another.