Throwing back to a beach-side moment, Bindi shared the heart-warming sentiment, "A love like this is eternal. Happy Anniversary to my extraordinary parents. ❤️"
Similarly, Robert shared a cute Australia Zoo couples photo with the caption, "Happy wedding anniversary Mum and Dad. Forever my biggest inspirations ❤️"
On her personal Twitter, Terri responded to her children's gorgeous messages with meaningful words of her own.
"It makes me happy to remember this special day," she wrote to Bindi.
"It’s been an incredible 31 years since that special day," she wrote to Robert.
The Irwin children echoed these very same sentiments for their parents' 31st engagement anniversary in February.
Bindi posted a throwback photo of her father hugging Terri and their dog Sui on the grounds of Australia Zoo.
"Best friends. Soul mates. True love.❤️ The most incredible parents. And of course, Sui," Bindi captioned the post.
Similar to his sister, Robert also shared a picture of his parents with the caption, "It was on this day 31 years ago that my parents got engaged and set in motion what would become a legacy larger than life. I love my mum and dad so much… I’m proud to be their son ❤️."
Commenters flocked to both posts to express their condolences for the siblings, while also sharing the impact the late Steve had on their lives.
"Your dad was the reason I love animals and have adopted them throughout my life," one wrote.
To celebrate the "soulmate" connection between the Irwin parents, Terri also shared a post of her own on Twitter.
"It was 31 years ago today that Steve asked, and I said “Yes!”. We were soulmates, best friends, and worked together on a mission of wildlife conservation. Best of all we had lots of fun!" she wrote.
Through their work at Australia Zoo, the Irwin family continue to honour Steve every day.