A bizarre 'S' shape which mysteriously appeared on Perth's weather radars - and was immediately dubbed the Rottnest Monster - has been explained as the result secret Defence training exercise.
Conspiracy theorists went into overdrive on Wednesday when the unusual formation appeared on the Bureau of Meteorology's weather radar.
The 'S' shape in the middle of the Indian Ocean, around 30km west of Rottnest Island, was theorised to be a cloud formation, a controlled weather pattern or even a massive flock of birds.
But a spokesman for Defence has now solved the mystery.
"The unusual pattern that appeared on the Bureau of Meteorology's Perth weather radar on Wednesday 12 February, was the result of a Defence exercise off the West Australian coast," a statement said.
"The exercise is a regular training activity involving ships and aircraft, that is designed to prepare a Navy warship for an operational deployment. This exercise is ongoing.
"The environmental conditions over the West Australian coast at the time of the activity provided a unique opportunity for this routine activity to be visible on the weather radar display."