Terri Irwin shares beautiful never-before-seen photo of Steve Irwin with his then-newborn son

Happy birthday, Robert Irwin!

The son of late Crocodile Hunter Steve Irwin celebrated his 16th birthday over the weekend, and his mum, Terri Irwin, couldn't resist celebrating with a beautiful throwback photo of the father-and-son duo.

Taking to Twitter, the 55-year-old shared a never-before-seen heartfelt snap of Steve cradling his then-newborn son.

"Happy 16th birthday, @RobertIrwin. Your dad would be so proud of you. He has loved you since the moment you were born," she captioned the photo.

While on Instagram, his 21-year-old conservationist sister, Bindi Irwin, also shared a sweet snap of Robert as a baby. 

"Happy 16th birthday to the cutest ducky I’ve ever known!" she wrote alongside the photo.

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"Robert, one of the best parts of my life is getting to be your sister. Thank you for being such a wonderful light in my life. You’re amazing and I love you! 🐥"

Robert celebrated his big 1-6 at the Australia Zoo, feeding crocodiles and blowing out candles on his rhino-themed cake.

Steve tragically died in 2006 after being struck by a deadly stingray barb while filming for one of his many TV shows off Port Douglas, when Robert was just two years old.

"When people say, 'You remind us of your dad,' it's the biggest compliment I could ever receive," Robert previously revealed.

"Because this is what we've dedicated our life to - making sure that that message that he had, that passion that he had, continues."

"He really did change the world. He inspired us. That's why we're so passionate," he added.