In 1995, two Australian friends, Casey Dean and Eduards Nits, purchased the Quarter Pounder with cheese from a McDonald's in Adelaide. At that time, Bill Clinton was the President of the United States. They had no idea that this simple purchase would turn the burger into a fast-food legend.

"We were teenagers and ordered way too much food," Dean told AFP. "We joked about keeping the burger forever."

The friends decided to keep the burger, which they fondly named "their mate." Now, nearly three decades later, the burger, nicknamed the "McFossil," shows no signs of mould or bad smell. It has only shrunk slightly from its original size.

"Even the sesame seeds are still on there, just a few have been knocked off," Dean said.

The McFossil's long life is surprising, considering its storage conditions. Most of the time, it was kept in a simple cardboard and wooden box. For over ten years, it stayed in a warm shed in Adelaide, where summer temperatures often rise above 30 degrees Celsius (86 degrees Fahrenheit).

"The rats had actually eaten through the plastic bag, heaps of clothes, got into the box, and they'd left the burger," Dean said.

Calling it the "Senior Burger" and still referring to it as their "mate," the two friends created social media profiles for the burger and even wrote a song about it.

They believe it is the oldest known McDonald's burger in the world, even older than a famous ten-year-old cheeseburger in Iceland that is displayed in a glass case and watched online by thousands.