Robert and Bindi Irwin share tributes to late dad Steve on his 64th birthday

Bindi Irwin and her younger brother, Robert, are paying tribute to their dad, Steve Irwin, on what would've been his 64th birthday.

The siblings took to social media to share birthday wishes to the late wildlife conservationist, who died nearly 20 years ago.

"Happy Birthday, Dad. We miss you so much," Bindi wrote on Instagram, alongside a carousel of throwback photos.

"Grace is so proud to tell everyone that Grandpa Crocodile is her guardian angel. Love you. Forever."

"Would have been your birthday today. Love you, miss you... thank you for being a guiding light and inspiration every day," Robert wrote on his own Instagram.

Steve - famously known as The Crocodile Hunter - died in 2006 after being stung by a stingray while filming on the Great Barrier Reef for his documentary series Ocean's Deadliest.

At the time of his death, Robert was just two years old, and his sister was eight.

Steve and his wife, Terri, were married for 14 years before his death.

In an interview with Men's Health, Robert, who took home the Mirrorball Trophy and won Season 34 of DWTS with his partner Witney Carson in December, opened up about representing a legacy that his parents created.

"When I step into the ballroom, I'm representing a legacy that my dad created with my mom. I'm representing everything I stand for, not only as a wildlife conservationist, but also as someone who is working really hard to try and spread some positivity and passion. I want to be a role model for young people."