Katy Perry's grandmother keeps her grounded.

The 'Wide Awake' hitmaker is amused by the fact that 91-year-old Ann Hudson - who appears in her new documentary film 'Part of Me 3D' - ''doesn't acknowledge'' her success and can't understand the fuss that surrounds her famous granddaughter.

Katy said: ''My grandmother is in the movie and she steals the show, she is living in Las Vegas and she doesn't acknowledge my success at all, which is exactly what I need.

''When she was at the Hollywood premiere she was like, 'Oh, why are you here?' and I was like, 'It's my movie,' and she was like, 'Oh is it?' She thought everybody was there to see her!''

The 27-year-old pop superstar is now planning to take a break from music because she fears being overexposed.

She added in an interview with The Sun newspaper: ''I will take a catnap, take a pause, plug into The Matrix - but I won't go away.

''What I need to do is let the dust Settle and take the temperature of what the world wants musically.

''I am definitely going to recharge because you can get over-exposed and I am balancing that tightrope at the moment, having my own movie about myself.''