Robbie Williams has been interviewed about his alien encounters for a new documentary.

The 44-year-old pop star will appear in 'Hunt For The Skinwalker' in which he will open up about his own experiences with extra-terrestrials.

The film has been made by Robbie's friend George Knapp - a journalist for Channel 8's I-Team in Nevada - and Jeremy Corbell and it probes the strange events that have occurred on the Skinwalker Ranch in Utah, which includes UFOs being spotted in the sky and cattle being mutilated.

There have also been reports of strange creatures roaming the area and they have been given the name 'skinwalkers' by the Native American Ute tribe, which is reference to a type of shapeshifter.

A source told the Daily Star newspaper: ''Robbie has had a number of encounters which cannot be explained by conventional science and he has always been very open about them.

''When his friend George asked him to be part of his film he agreed instantly, he isn't embarrassed by his belief.''

Robbie - who is married to American actress Ayda Field, who is going to be joining him on the new series of 'The X Factor' - spent some time actively hunting aliens when he took a break from his music career in the later 2000s.

The 'Angels' singer claims he once saw a UFO so close to him he could've hit it with ''a tennis ball''.

He said: ''I've seen one right above me and if I got a tennis ball out I could have hit it with a tennis ball. No substance was involved. No, no substance was involved at all.''

And extraterrestrial expert Michael Luckman - the Director of the New York Centre For Extraterrestrial Research - claimed that he believed Robbie had become a ''point man'' on Earth for alien visitors.

Luckman previously told BANG Showbiz: ''Robbie is now becoming a point man for contact with extraterrestrials. None of the experiences I've seen are in the same category of what Robbie appears to have experienced. Robbie could easily disappear and then come back as an ambassador for their race. He is the first celebrity I know of to actually go out there and actively hunt for alien life forms. He's unusually pro-active, even putting his musical career on hold. And he is more likely to make contact because of where he is spiritually - he takes it to the max.''