Katy Perry says her "tummy turned" watching scenes from her upcoming movie Part of Me 3D.

The singer is currently promoting the fly-on-the-wall documentary, which was produced from over 300 hours of film footage shot during her 2011 California Dreams world tour.

The Wide Awake star admitted it wasn't easy watching the final edit, especially because she was dealing with the breakdown of her marriage to comedian Russell Brand at the time of filming.

But Katy wanted to show her true self, with all of her issues and insecurities to create an honest movie.

"Sometimes my tummy turned when I saw different scenes - whether I was upset, whether I looked completely awful and exhausted, bloated with zits, [the] whole bit," she told ET Online. "I left them in there 'cause I thought it was important to show the truth because there's a lot of fakeness out there these days."

Katy also revealed just how much she struggled to keep performing during her marriage breakdown.

Her estranged husband announced the couple was separating towards the end of the star's epic 124-date tour, with some reports claiming the 27-year-old was unaware he had decided to divorce her.

"There were times on the road where I literally had to throw myself on that [stage] lift and kind of flip a switch and separate the personal from the professional because it's my personal problems not the audience's problems," she said. "[The movie] is about overcoming obstacles no matter what shape they come in. Sometimes the obstacle is your job or the people around you... and then sometimes it's your personal struggle."