Was it a Russian plane or even a UFO? No, it was an RAF aircraft on training
Some thought it was a Russian spy plane, others said it was a UFO.
Now the mystery of a large, low-flying aircraft spotted along Northern Ireland's coast on Tuesday has finally been solved.
The aircraft, which sparked a flurry of excitement and speculation because of its size and low flying altitude, has been identified as a RAF C130-J Hercules.
The military plane, which is usually the prime transport for parachuting troops and equipment into hostile areas, was on "a low level training flight", according to the MoD.
Sightings of the aircraft on Tuesday afternoon caused a stir on social media. Even the police were asked by stunned eyewitnesses to find out what was going on.
After some detective work, Newry and Mourne police solved the mystery and shared their findings with their curious Facebook followers.
"Mystery solved. I've made some enquiries with the MoD and they confirmed that there was a military aircraft flying in these areas yesterday and was conducting low level navigation training," one officer wrote.
He added: "Sure where else would you want to be but in NI on a glorious day like yesterday, the crew would definitely have enjoyed the views... No need to go to any of the air shows now!"
The aircraft was spotted in Ballycastle, Newry, Warrenpoint, over the Mourne Mountains and over the dual carriageway between Portrush and Ballymena.
While many amateur plane spotters couldn't believe their luck, other eyewitnesses were left troubled.
Margaret Rafferty wrote on Facebook: "Flew right over my house out in Lissummon. I actually ran outside to see were kids ok cause I thought it was going to crash it was that low".
Keira McLeod, who spotted it flying over the Mourne Mountains, said: "It looked like something from a movie. Truly Spectacular".
Colleen Ward wrote: "Yes it was unbelievable! ! Alarmingly low... has caused anxiety today all round... great to see but jez it was low... ran for my kids also as I was sure it was heading straight into our house. Not something I expected to see today."
Erica Maxwell who saw it in Augher, Co Tyrone at about 5pm on Tuesday said it "scared the life out of the kids."
The Lockheed C-130 Hercules is a four-engine turboprop military transport plane capable of using unprepared runways for take-offs and landings. The versatile airframe has found uses in a variety of other roles, including for humanitarian aid, search and rescue, scientific research support, weather reconnaissance, aerial refuelling, maritime patrol and aerial firefighting. The Hercules has been flying since the 1950s and has the longest continuous production run of any military aircraft in history.