Ashleigh Sullivan, 19, said she had given up hope of ever finding Clyde after he vanished from her family home near the city of Hobart in Australia's island state of Tasmania when he was about a year old.
"I'm positive he remembers. He's not acting like he's suddenly appeared somewhere and is frantic," Ms Sullivan said as she tearfully held her contented cat following his unexpected return.
A nurse apparently found Clyde wandering at a hospital in the remote Queensland state town of Cloncurry.
Thinking he was a local stray, she cared for him for four months. But she finally took him to a local veterinary surgeon because she was leaving town and did not want to take him with her.
The vet, Donna Weber, traced Clyde's owner from an identification microchip embedded under his skin.
But as yet no-one has a clue how Clyde managed the 185-mile sea journey across the Bass Strait from Tasmania, off mainland Australia's south-east coast, and then made an additional distance of 2,000 miles overland to Cloncurry, deep in the arid interior of the Outback.
An animal transport company returned a contented Clyde to Hobart for free – flying most of the way.
"It's pretty special to have him back." Ms Sullivan said. "I'm overwhelmed."