Robbie Williams once saw a UFO so close to him he could've hit it with ''a tennis ball''.

The 44-year-old singer insists he hadn't been taking any ''substances'' when he spotted the unidentified flying object, and he has seen a number of ''intriguing and powerful'' sights in his time.

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.''

The 'Angels' hitmaker is always amazed when he has a UFO experience and just ''can't explain'' why he is able to see such ''phenomena''.

Speaking on '60 Minutes', he ''I've seen a few strange things. I've experienced phenomena I can't explain.''

Last year, Robbie recalled spotting a UFO just 150ft ''above [his] head'' when he was ''totally sober''.

He said: ''I've seen stuff that I can't explain ... I've had a UFO right above my head, totally sober. Less that a 150ft above my head and there it was.''

In 2008, Robbie recalled once seeing ''two big massive balls light'' above his head when he was in America.

He said: ''I was at the Beverly Hills Hotel and I was lying on my sun lounger outside at night, looking up.

''Then, about 300 foot above me, there was this square thing which just passed over my head silently and then shot off.''

But the 'Let Me Entertain You' hitmaker - who has daughter Teddy, five, and three-year-old son Charlton, with wife Ayda Field - is not the only star who has had such sightings.

Kendrick Lamar puts his musical talent down to seeing an alien when he was six years old.

He said: ''Nobody believed me then and they don't believe me now.

''It's just something I can't really describe, because it just sounds like, 'OK, you just seen a dart go past.' That s**t don't make sense.'

''That's probably why I'm doing music right now. Who knows. They probably gave me the energy.''