Irwin, who was nicknamed “The Crocodile Hunter” due to his television series of the same name, passed away in 2006 at the age of 44.
Robert shared a black and white photograph on Twitter and Instagram of himself with his father, sister and mother Terri Irwin.
The picture, which the teenaged wildlife photographer captioned “Family Always”, depicts the family-of-four on a rocky landscape.
Bindi, who last year announced her engagement on her 21st birthday, posted a throwback picture of herself with her father, who is wearing an Australia Zoo shirt in the image.
“Dad, today is your birthday,” she wrote in the caption. “I had an extra strong cup of tea just how you liked it. I hugged Mum for you and told her how much we love her.”
The former Dancing with the Stars winner wrote that she and her brother went on a hike through the mountains that their father “cherished”, in addition to watching one of his documentaries and sharing stories about him with others.
“I walked through your office in the zoo and smiled at our old family photographs,” she stated. “Today and every day I miss you and love you beyond description. You’re always with me.”
Robert and Bindi’s mother Terri, who married Irwin in 1992, expessed how her “heart aches” missing her late husband in a statement shared on Twitter.
“Today would’ve been Steve’s 58th birthday. While my heart ache missing him every day, I’m determined to celebrate what he loved the most,” Terri wrote, alongside a series of photographs.
“He was my best friend, best dad and built the best zoo. I love you.”
Today would’ve been Steve’s 58th birthday. While my heart aches missing him every day, I’m determined to celebrate what he loved the most. He was happiest spending time @AustraliaZoo w/ @BindiIrwin & @RobertIrwin. He was my best friend, best dad, & built the best Zoo. I love you. pic.twitter.com/IWsoWuJqxY— Terri Irwin (@TerriIrwin)February 22, 2020
Numerous people expressed their admiration for Irwin on social media.
“Your dad was my role model while I was growing up, and he still is,” one person commented on Robert’s Instagram post.
“Family of legends,” another wrote.