Rocos, now 50, writes in "The Power of Positive Drinking" that Diana donned a military jacket and policeman's cap and ordered drinks at the Royal Vauxhall Tavern in London without being recognized.
"When we walked in ... we felt she was obviously Princess Diana and would be discovered at any minute," Rocos says. "But people just seemed to blank her. She sort of disappeared. But she loved it."
"She did look like a beautiful young man," Rocos recalls. “She did look like a beautiful young man. She was always a very fit girl, so they might have thought, ‘There’s a nice young man with pert buttocks’.”
Earlier that night, the foursome had watched "Golden Girls" reruns together. When Diana asked about going out with them, Rocos and Everett worried that the young royal would get caught.
But Mercury encouraged her: "Go on, let the girl have some fun."
The NY Daily News points out that Rocos is the only living participant of the charade, so there's no way to confirm the report. Freddie Mercury and Kenny Everett died of AIDS-related illnesses in 1991 and 1995 while Diana died in a 1997 car crash.