Benji Madden "couldn't be more proud" of Cameron Diaz.

Benji Madden and Cameron Diaz

Benji Madden and Cameron Diaz

The Good Charlotte rocker is "always amazed" by his 43-year-old spouse - who he married last January after eight months of dating - and is thrilled she is preparing to release her new book, 'The Longevity Book', in April.

Sharing a picture of the tome's cover, he wrote on Instagram: "I Couldn't be more proud of my Bad Ass wife.

"She wakes up everyday on a mission to try and make the world a better place.

"I'm always amazed by the courage, strength and vulnerability she shows, relentlessly encouraging other women to love themselves. It has been amazing to get to watch her journey with her New book! #theLongevityBook #April5th @thebodybook @camerondiaz #lovemywife.(sic)"

The 'Mask' actress went bare-faced on the cover of the book and is thrilled with how it looks.

Revealing the cover for the first time on Instagram last week, she wrote: "I am so excited I can barely contain myself!! As soon as I saw it myself, I wanted to share with you the cover of THE LONGEVITY BOOK.

"I am so proud of this book and very much looking forward to engaging us all in a new conversation about aging - how to do it with strength, grace, health and wisdom.

"I also wanted to thank you again for your beautiful submissions, which we'll eventually get to show you as part of the cover beyond the cover; a perfect representation of women standing beside other women, as a united front, to stage change and incite progress. I can't wait until hard copies hit the stands in April so we can really get started!! (Sic)"