The SSPCA rescued the swan, nicknamed Spike, from Loch Lomond, after he was found covered in cooking oil.
Swans mate for life and locals told the charity, Spike had recently lost his mate.
After cleaning up his feathers, staff at the National Wildlife Rescue Centre in Clackmannanshire paired him with a female swan named Sally, who had been rescued after she swallowed fishing tackle. The pair have become inseparable.
Centre manager Colin Seddon said, "He seemed very sad. He was very lethargic and down when he arrived
"However, he became a lot brighter when we paired him with a female swan named Sally after he was washed in our specialist oiled bird cleaning unit.
"Sally was rescued after swallowing fishing tackle which hadn't been disposed of properly and had an operation to remove the hook safely.
"The pair quickly became inseparable and there was immediately a noticeable change in Spike, who was clearly a lot happier.
"Spike was returned to Loch Lomond along with Sally and we hope they will stay together for the rest of their lives."
Anyone who discovers an injured or distressed animal should call our Animal Helpline on 03000 999 999.