Rocker Joan Jett apologized to Kristen Stewart after reportedly reducing her to tears during a heated confrontation on the set of upcoming biopic The Runaways.

The pair have struck up a friendship since Stewart signed on to play the I Love Rock N Roll hit-maker in a new biopic about her 1970s band.

However, the actress allegedly broke down crying after Jett gave her a 'hard time' during filming in a bid to improve her performance - prompting the rocker to apologize.

A source tells the New York Daily News, "Joan just wants Kristen to play an authentic version of herself, so she needled her a little bit too much. But she apologized when she realized how upset Kristen got."

In April, the Twilight actress admitted she was feeling the pressure that comes with playing a real person onscreen: "It's one of the most immense responsibilities to play a real person. Her story's important. It's an incredibly triumphant feminist story really."

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(This news article provided by World Entertainment News Network)