Steve Irwin's Heartfelt Letter to His Parents Discovered: 'My Love for You Is My Strength!'

The late Crocodile Hunter was eternally grateful to his parents.

Steve Irwin left behind a touching letter to his family.

The late Crocodile Hunter penned a heartfelt note to his parents, Bob and Lyn, expressing his love and admiration for them. The letter, which was tucked away in a book, was discovered this year and published in Bob's new memoir, The Last Crocodile Hunter: A Father and Son Legacy.

WATCH: Bindi Irwin Graduates College! Plus, She's Writing a Book and Getting Her Own Place! 

"Probably one of the most unfortunate things in a 'Bloke's Life' is that it takes over 30 years to realize how essential you have been to build my character, my ethics and, most importantly, my 'HAPPINESS,'" Irwin wrote, 12 years before his untimely death in 2006. "At 32, I am finally starting to figure it out. In good times and in bad, you were there. Your strength and endurance to raise me will not go unrewarded."

"My love for you is my strength!" the letter continues. "For the rest of my life I will reflect on the unbelievably GREAT times we've shared and will continue to share. You're my best friends!" 

Allen & Unwin Books

On the envelope, Irwin had written: "Please be happy to know that your strength and wisdom have been passed on," according to the BBC.

The famous wildlife expert was killed on Sept. 4, 2006, after being pierced in the chest by a stingray. At the time, he was filming an underwater documentary titled Ocean's Deadliest in Queensland, Australia. The Last Crocodile Hunter: A Father and Son Legacy will be released on Oct. 25.

WATCH: Bindi Irwin Pays Tribute to Her Mom and Late Father While Celebrating 18th Birthday 

Irwin's daughter, Bindi, recently celebrated her 18th birthday and took to Instagram to celebrate the milestone occasion with a super sweet throwback photo and a touching tribute to her late father.

"Life has changed in a million ways since this photograph was taken," she wrote. "Along the way we gained another incredible part of our family, my brother Robert. Our conservation work with Wildlife Warriors took off around the world. Our home, Australia Zoo continued to expand and has become the greatest zoological facility on planet earth. Our Dad, Mum's soulmate and a superhero for us all, passed away."

"However, since this photo was taken, 18 years ago, one life ingredient has remained, unchanged, unbreakable," Bindi added. "That is the unconditional love that is shared between my beautiful little family and the loyalty we have to each other and everyone else who has taken this journey with us."

For more on Bindi's touching tribute to her dad, watch the video below.