It was reported at the time that the pair were watching "The Merry Widow" when the alleged altercation took place.
According to the Sydney Morning Herald, Nicole and Keith - along with most of the audience - were giving a standing ovation at the end of the show when the man sat behind them asked them to sit down. The man then "swatted" Nicole with his programme before Keith accused him of "assaulting his wife."
During an interview on KIIS FM's "Kyle and Jackie O" show on Friday (26Feb21), Keith explained what had happened as he told the hosts, "I looked around and I see a few people standing and a few more and I thought 'oh I'm getting up.' And then this guy behind me just whacked Nic, like really hit her, with the program."
"It's a bit of a pickle I was in because I'm a husband and you want to defend your wife but it took a lot of restraint. I was pretty upset."
Keith added that as the performance was the first time he'd been to the opera, he was unaware of the "etiquette" involved.
"We did not know you are not supposed to stand in the opera. Having not been to the opera before ever in my life, I am sensitive to the etiquette," he added.