Katy Perry's grandmother took over a Las Vegas theatre to watch the singer's new movie with 65 friends.

The star is currently promoting Katy Perry: Part of Me, which follows her epic California Dreams tour, but also captures the breakdown of her marriage to Russell Brand.

Katy is very proud of the documentary and has revealed her family are equally as excited about it.

She took to her Twitter account to reveal 91-year-old Ann Hudson had rounded up a huge group of pals to go and see the movie this week.

Katy shares a close bond with Ann, who also appears in Part of Me.

The 27-year-old singer recently revealed her grandmother "steals the show" in the documentary.

Ann accompanied Katy to the movie's Hollywood premiere, and Katy credits the older lady for keeping her grounded despite her success.