A YouTube video from The Dodo, called Clownfish Named Nemo Has 10-Year Friendship with This Diver shows footage of a New Caledonian scuba diver, Marino, who claims to have a special relationship with a clownfish, who will come out of the reef when summoned, and interact with the diver.
Fishlore explains clownfish usually don't live this long - but it is possible.
Lifespan : 3 - 6 years generally, but see comment below from Dudley who has a pair of percula clowns that has been alive for 27 years!
They also say that tank-raised clownfish tend to live longer.
Is this story true?