Pattinson, 27, and Perry, 28, were seen in the back of a courtyard at San Ysidro Ranch, taking in the wedding rehearsal of a pair of strangers, reported People magazine.
"Katy and Rob were just sitting next to each other watching the wedding rehearsal in the main courtyard area. They were dressed very casually. She was wearing a hoodie and big sunglasses. There was no PDA (public display of affection) between them and no body language that showed they were dating. They just sat together and watched," a source said.
"Perry felt that Stewart's cheating scandal with married director Rupert Sanders had irreparably damaged the relationship," the source added.