Leo couldn't stop laughing at how young he looked in the 1997 blockbuster.
Leonardo DiCaprio's "tusk" task
Leonardo DiCaprio is leading a campaign to save elephants and stop the international ivory trade.
DiCaprio, global ambassador for the programme, said: "Many people around the world still have no idea that elephants are killed for their ivory tusks, and that's why public education is so important.
"There were 1.3 million elephants in 1979; rampant poaching and other factors have reduced that by more than half to an estimated 500,000."
He added: "Authorities in 85 countries have seized almost 400 tonnes of ivory on the black market since the 1989 ivory trade ban."
IFAW president Fred O'Regan said: "We are honoured to have Leonardo's support for our Animal Action campaign to stem the ivory trade. With his help, we hope to create a groundswell for elephant protection that can't be ignored."
Find out why the Hollywood hunk won't wear antiperspirant.
The pair will reunite on the big screen for a fifth time in The Wolf of Wall Street.
The actor has reportedly insisted that he is not bothered by his lack of success at the Academy Awards.