An obese eight-year-old black Labrador has now lost 20kg (44lb) in weight by running on an underwater treadmill at a fat dog boot camp in Devon.
When Prince started attending the rehab centre in Dawlish five months ago, he weighed 75kg (184lb).
He was put on a special diet, including fasting one day a week, and now weighs 55kg (121lb).
Other techniques the Linhay veterinary clinic uses to rehabilitate pets include Pilates and acupuncture.
'Chasing pheasants'
Linhay vet Kate Rew said Prince was now in "great form".
"He actually runs around chasing pheasants now," she said.
His target weight is 35kg (77lb).
Because of his weight Prince has had to have surgery for ligament disease in his knees, which he developed due to his weight.
He now has acupuncture to control the pain and to enable him to exercise.
Other health problems Prince has include poor cardiovascular fitness and the inability to control his body temperature.
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