BRUSSELS (AFP)— An unidentified flying object photographed high in the Belgian sky that puzzled even NASA scientists turns out to have been a fake made out of foam, the man behind the hoax said Tuesday.

Though scientists pored over the picture of a triangular-shaped flying saucer with four lights, allegedly photographed in April 1990 by a young worker, the mystery remained intact until the man's revelation on the RTL-TVI network.

Made of polystyrene in a matter of hours and photographed that night, the picture was released after several sightings of UFOs over Belgium in 1989 and 1990.

Then aged 18, the man identified only as Patrick said he and a few friends "made it, painted it, hung it up and then photographed it".

The photo was the sharpest available to experts in a two-year period in which thousands of people across Belgium reported UFO sightings.

Several days after its release, a Belgian airforce plane was ordered to hunt down the UFOs across the country, but to no avail. Some believed the UFOs were new stealth fighters being tested by NATO.

"It's too easy to fool people, even with a cheap model," said Patrick, adding he had decided it was time to come clean.