Willem Duyn, known professionally as Big Mouth, was a Dutch singer who, together with singer MacNeal, represented the Netherlands in the Eurovision Song Contest 1974 in Brighton, England with the song I See A Star, which finished in third place.

They began their career in 1971, achieving huge success. MacNeal temporarily embarked on a solo career while Big Mouth formed a new duo with a new singing partner, called "Big Mouth & Little Eve".

In the 1990s, Big Mouth joined several rock bands but in their final years they mostly played cafés and bars.

He died of a heart attack in December 2004 at the age of 67.

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