French emergency services were deployed and crews from numerous ferries joined a search attempt when a pensioner jumped overboard a P&O Ferry.
The incident, last Thursday, happened just before the 7.15pm sailing from Dover entered the Port of Calais, at about 9.45pm local time.
The body of a man in his 70s was later discovered by crew from another ferry.
Christopher Henwood was a passenger aboard the Pride of Burgandy when it happened.
They were alerted to the incident by the captain of the ship.
Mr Henwood said: “Just as we were going down to the car decks, we were told we had to report back to the information desk so they could check our names against the manifest.
“We were held on board for about an hour.
“Then the captain announced they had recovered a body.”
Brian Rees, a spokesman for P&O Ferries, said: “An elderly gentleman, in his seventies, climbed over the ship’s rail and jumped into the water just as the ship made its entrance to the port.
“Various ships quickly launched their rescue boats to try to retrieve him but it was about 90 minutes later when crew from one of the French ferries, Nord Pas de Calais, found the body”.