The duo was in the limelight in July 2012 for having an affair following their meetings on the sets of the movie 'Snow White And The Huntsman'.
However, after a lot of criticism, Stewart's boyfriend Robert Pattinson took her back, but Sanders' model wife Liberty Ross has filed for a divorce.
"Rupert's reached out to Kristen, but she doesn't want anything to do with him. He texted her a number of times after Liberty filed for divorce, however Kristen didn't respond," thesun.co.ul quoted a source as saying.
"In truth, she regrets ever getting involved with Rupert, because of how much it hurt Robert and the amount of public backlash she was subjected to," the source added.
Meanwhile, Stewart is still trying to bring back the lost romance with Pattinson.
"Kristen doesn't really know what's going on with her and Robert at the moment, and she's been left in limbo. Ideally, she would like things to go back to how they once were, but that's proving a lot more difficult than she imagined," a source said.