He also shared a photo showcasing how he spent the day -- feeding crocodiles!

\"You know it’s going to be a great birthday when it starts by feeding a croc!\" he captioned his post. \"Thank you to everyone who came out to @australiazoo today.. it meant the world to celebrate with you all!\"

View this post on Instagram

You know it’s going to be a great birthday when it starts by feeding a croc! Thank you to everyone who came out to @australiazoo today.. it meant the world to celebrate with you all!

A post shared by Robert Irwin (@robertirwinphotography) on Dec 1, 2019 at 3:49am PST

Robert's mother, Terri Irwin, posted a loving message for her son on Twitter, featuring a photo of her late husband with Robert.

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

Happy 16th birthday, @RobertIrwin. Your dad would be so proud of you. He has loved you since the moment you were born. pic.twitter.com/FhwnQRJtA7

— Terri Irwin (@TerriIrwin) November 30, 2019

She also posted a collection of photos of Robert with his animal friend, Jenny the snake, to mark the occasion.

Growing up @AustraliaZoo means always having special friends. Jenny has been @RobertIrwin’s pal for 16 yrs tomorrow. Happy almost birthday! pic.twitter.com/I40HgpNa8I

— Terri Irwin (@TerriIrwin) November 30, 2019

Robert's sister, Bindi, shared what she feels is \"one of the sweetest photos ever taken.\"

\"My whole world,\" she captioned a photo of her mother with Robert. \"It’s incredible that Robert is sixteen now, time sure does fly. Also, Mum is the most beautiful woman in the world.\"

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One of the sweetest photos ever taken❤️ My whole world. It’s incredible that Robert is sixteen now, time sure does fly. Also, Mum is the most beautiful woman in the world.

A post shared by Bindi Irwin (@bindisueirwin) on Dec 1, 2019 at 6:22am PST

The bride-to-be also shared a throwback of Robert in an adorable costume. \"Robert, one of the best parts of my life is getting to be your sister,\" she wrote. \"Thank you for being such a wonderful light in my life.\"

View this post on Instagram

A post shared by Bindi Irwin (@bindisueirwin) on Nov 30, 2019 at 11:25am PST

\"You’re amazing and I love you!\" she added.

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