Robert Irwin/ Instagram
The Australian conservationist celebrated her sibling on Instagram on Wednesday (which was Thursday morning — his birthday — in Australia).
"Happy Birthday to the taller Irwin sibling and greatest brother in the world," Bindi wrote alongside a photo of the two jokingly acknowledging their height difference. "You light up our lives with your hilarious sense of humour and kind heart."
Referencing their father, Steve Irwin — who died in 2006 at age 44 — Bindi continued: "I see so much of Dad in everything you do and I know he would be beyond proud of you. We all are. Thank you for being such a good uncle to Grace and fantastic brother to me and Chandler."
"We love you and can't wait to celebrate today!" she concluded her post.
Robert responded in the comments: "Love you B 🧡😊 thank you!"
The siblings are close friends, and last month, Robert revealed his sister's been hoping he'll start dating soon.
"It's pretty funny because of course, my sister has gotten married and had a kid and there's always a lot of rumors that go around," he told E! News. " 'Bindi's having a second kid' or 'they're having triplets.' "
Robert Irwin/Instagram (Left to right) Bindi Irwin, Robert Irwin and Steve Irwin
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Robert added: "There's always so many crazy things that happen so Bindi always says, 'Robert, it's your turn now. You gotta find someone to take the heat off me!' "
The animal conservationist — who created a new photography book titled Robert Irwin's Australia — said that he doesn't have any "big scoop" to discuss when it comes to his current relationship status, but will "get there" eventually.