Cameron Diaz turned 45 on Wednesday (August 30) and her husband Benji Madden honoured his wife on her big day with a super-sweet birthday message.

Posting a cute pic of the couple together, Benji declared he was the “luckiest guy alive,” because he’s married to Cameron.

“Happy Birthday to my Beautiful Wife. I feel like I am the LUCKIEST guy ALIVE," Madden captioned the pic, which shows the couple cuddling on a boat.

"I don't think anyone could ever know the Depth, Kindness, and Compassion that I get to experience everyday thanks to My One and Only,” he continued. "You got me til the end, baby.”

Benji and Cameron married in January 2015, in a spontaneous ceremony less than a week after the guitarist popped the question on Christmas Day.

The couple rarely discuss their relationship on social media, instead saving it for moments when they give each other a special shoutout.

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Last year, when Cameron released her second book, The Longevity Book: The Science of Aging, the Biology of Strength, and the Privilege of Time, Benji took to Instagram to share how proud he was of his wife.

"I couldn't be more proud of my Bad Ass wife," Benji wrote at the time. "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!”