Steve Irwin's heartfelt letter to his parents discovered: 'My love for you is my strength!'

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."

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"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!"

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.