Pharrell Williams has put pen to paper on a deal to release a series of children's picture books.

The singer has teamed up with publisher Putnam Books for Young Readers to create four releases.

The first will be named Happy after the US star's hit 2013 single.

It will feature photos of children "celebrating what it means to be happy" and it will have a print run of 250,000.

The book will be released on September 22.

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Watch Pharrell's 'Happy' video below: