Actor-turned-author Hill Harper has decided to put the pen down and stop writing books to focus on his other ventures.

The Csi: Ny star reveals his fifth book, Letters to an Incarcerated Brother, will be his last.

He tells U.S. breakfast show Today, "I put everything I had into Letters to an Incarcerated Brother.

"This is a motivational book for incarcerated individuals and their families and hopefully any other people that are in any type of prison, whether it be a job that's got them stuck or death that's got them stuck, so I couldn't be more proud of this book. It's by far the best book I've written and... this is it."