Robert Rodriguez has said that he was "blown away" by Lady Gaga's acting skills.
The director first worked with the pop icon on Machete Kills, before offering her a cameo in Sin City 2: A Dame to Kill For.
Rodriguez told E! News: "I told her she had to be in it [Sin City 2]... The camera loves her.
"She's a great performer. She's performed twice for me now and I was blown away by her discipline. She studied acting before she became a singer and you could really tell."
He also told of the element of chance involved: "She happened to be on tour in Houston, just a couple of cities away from us in Austin. She was ready.
"She brought her own wigs! I said, 'We're not going to have time to make a wig for you.' She showed up, we did the scene, she knocked it out of the park and then she was back on tour."
Sin City 2: A Dame To Kill For stars Jessica Alba, Eva Green and Josh Brolin, as well as Bruce Willis and Mickey Rourke, and will be released on August 29.