Tiller was days old when he was spotted in distress at North Queensferry by men working on the new Forth crossing.
But he has now been returned to the water at Silver Sands, Aberdour where seal colonies are nearby thanks to the Scottish SPCA who cared for him for three months.
Colin Liddell, from National Wildlife Rescue Centre near Alloa, said: "Tiller was our first grey seal pup rescue of the season, and he's now one of the first to be released back into the water after a very successful period of rehabilitation.
"He was accompanied by another male pup, named Ferry, who came into us at the beginning of November from Uist. He too was only around 13kg when he first arrived but both pups were great feeders and put on plenty of weight in our care.
"We're confident both boys will join up with the local colonies and help maintain the grey seal population we have on the east coast of Scotland and around the Forth Estuary."
The Scottish SPCA said it has rescued 53 grey seal pups so far this winter, almost 40 per cent more than the number rescued by the same time last year.
Mr Liddell added: "We can't say for certain what is responsible for the increase.
"It may be due to the stormy weather we've had lately, washing pups off their pupping grounds before they're old enough to enter the water."
Anyone who spots an injured or distressed seal pup on the shore can call the charity's animal helpline for advice on 03000 999 999.