On Sunday afternoon, the famous pair were spotted watching the wedding rehearsal of two strangers at San Ysidro Ranch in Santa Barbara, not far from where the Fireworks singer grew up.
"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 (public display of affection) between them and no body language that showed they were dating. They just sat together and watched.
"They were not affiliated with the wedding party and were not seen mingling with guests."
Katy, 28, who is also single following her split from John Mayer, is no doubt helping Robert recover from his recent heartbreak. Last week, the English actor moved out of the house he shared with his long-term girlfriend Kristen Stewart.
He recently ended his relationship with his former Twilight co-star — who had a brief affair with married director Rupert Sanders last summer — after friends, including Katy, told him he deserved better.
A source told Life & Style magazine that Katy was never a fan of the couple's reconciliation. "Katy never really supported Rob's decision to get back with Kristen. She always said they wouldn't last.
"Katy told Rob she didn't think their relationship could withstand the cheating scandal. And he deserved better than someone who would destroy a family (like Rupert's).
Despite the couple managing to patch things up after Kristen's "momentary indiscretion" last year, it's thought their relationship is over for good after Rob was spotted moving his things out of her Los Feliz home.