John explained that his co-star had severe intestinal problems, causing one to burst and fill her body with toxins.
“By the time someone got to her and realised she was in trouble, it was just too late."
The Wheel of Fortune star also sadly recalled witnessing her final moments.
“We went straight up to the hospital and sat with her, she was in a coma. She just looked awful, it was heartbreaking," John said.
“My wife said that when I leaned over and said, ‘Burgo is here, Adri’, she said her eyes opened briefly. But I didn’t see it, I was too busy bawling," the TV host said.
“I think it was about quarter past four in the afternoon we left the hospital, and she died half an hour later," he added.
John also opened up about how difficult it was to see his co-star in that state, noting that he hardly recognised her.
"She was a delight to work with," John said.
“She was always very outgoing and giving, she couldn’t do enough for people. We just hit it off from day one.”
The pair had one of the longest-running partnerships in Australian television, working on the Wheel of Fortune from 1984 to 1996.
John also opened up about how his co-star struggled after leaving Wheel of Fortune.
WATCH: Inside the secret life of Adriana Xenides
“That was the start of her downward spiral really. She found it really, really tough after having done it for so long," he sadly confessed.
John believes age shouldn't be a fact when it comes to hosting television, making note of Pat Sajak, the 72-year-old-host of the American Wheel of Fortune.
“America hangs on to their personalities,” he also said.
“They become part of their families. When you turn on your television, you expect them to be there.”
When asked if he would host Wheel of Fortune again, John replied, “Never say never."