Bilson and Roberts both attended the Refinery29 Third Annual 29Rooms: Turn It Into Art event on September 7 in Brooklyn.
We're told Bilson was mortified when she saw Roberts was at the event too and made sure to steer clear of the "American Horror Story" actress ... especially since she had just split with Christensen days before.
The Blast revealed the bombshell news that Bilson ended her longtime relationship with baby daddy Christensen after she found text messages between him and Roberts. She believed they were having an inappropriate relationship.
What's interesting, even though Bilson and Christensen had already split, the news of their relationship ending did not go public until two weeks later. Bilson was able to avoid the drama that would have surely erupted if it was known Roberts was at the center of the breakup.