The animal – named Hubble – was found in April at Camber Sands. Rescuers said he was not moving and had blood around his face.
He was treated by RSPCA Mallydams Wood Wildlife Centre and is now fit enough to be released back into the wild.
The one-year-old male had been suffering from lung-worm, the RSPCA said.
On Wednesday afternoon (May 12), Hubble was released back into the sea on Pett Level beach.
Here are some pictures from his release.