A guest at the wedding rehearsal at San Ysidro Ranch in Montecito, Calif., said the bride initially spotted the pair.
"Katy and Rob were just sitting next to each other watching the wedding rehearsal in the main courtyard area," rehearsal guest Stephanie Sands told people. "They were dressed very casually. She was wearing a hoodie and big sunglasses. There was no PDA between them and no body language that showed they were dating. They just sat together and watched."
Perry and Pattinson have been friends for years, and the two have been seen together with increasing frequency since Pattinson split with his Twilight co-star Kristen Stewart earlier this month.
But Perry has been open about her interest in her longtime friend, telling friend she would "love to date him" if he became single. And sources say the "Wide Awake" singer may have been a factor in the breakup when Stewart grew insecure over Pattinson's "clear to everyone" crush on Perry.