"One of the things I’m most thankful for was the passion for wildlife that he instilled in me at such a young age. He taught Bindi and I the importance of treating every living being as you would wish to be treated 💙."
The young Wildlife Warrior's words were soon met with a wave of support in the comments below.
Front and centre was Rob's big sister Bindi, who simply added "❤️❤️❤️" to her younger brother's tribute.
Meanwhile, American actress Emmy Perry was also visible in the comments, penning, "What a beautiful legacy he created! ♥️🐨"
"I'm 3000% sure that your Dad is very very proud of you Robert🤍" another supportive fan wrote.
"He really was an amazing person and would be so proud of you and Bindi! ❤️" added another.
One person not celebrating Father's Day with the Irwins is Steve's father Bob, who shares an estranged relationship with his daughter-in-law Terri and his grandkids.
Bindi has recently shared insight into the full extent of their rocky relationship.
WATCH: Chandler Powell cracks hilarious dad joke with Robert Irwin (Story continues after video)
When a fan asked why Bindi excluded her grandfather from her Father's Day tribute, Bindi showed her vulnerable side in a since-deleted social media comment.
"I really wish that my entire family could spend time with Grace. Unfortunately, my grandfather Bob has shown no interest in spending time with me or my family."
She went on to reveal that her grandfather has returned gifts she sent him after opening them.
"He has ignored me, preferring to spend time doing anything else rather than being with me,” Bindi wrote. "He has never said a single kind word to me personally. It breaks my heart."