Stewart had a fling with married director Rupert Sanders in 2012, leading to a brief break-up with her boyfriend Pattinson. Watson believes "everyone makes mistakes".
"Kristen is human, just like everybody else, and she's so young. Everyone makes mistakes, everyone. It's not fair to consider them matters of public interest," contactmusic.com quoted the 22-year-old as saying. "On one hand, I can understand why it happened: people felt really involved in her relationship with Robert Pattinson. But it's also true they both have done everything in their power to keep their relationship as far from the public eye as possible," she added.