Robert Irwin thanks his lucky stars for who he has as a sister.
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“Happy #NationalSiblingsDay! I’ve got the absolute best sister — Grace definitely has an amazing mum,” he captioned the picture.
Bindi, 22, shared the love in her own Instagram post, with a throwback photo of her and Robert, 17, as little kids.
“I’m thankful every day that I get to be your sister. Thank you for being such a wonderful friend and light in my life,” she wrote, while using the hashtags #Flashback and #NationalSiblingsDay.
Mom Terri Irwin also got in on the act Monday while honoring National Pet Day on Twitter. She shared a series of pictures with her kids, as well as one with her and late husband Steve Irwin and another with Robert, her and Powell.
"More like National Friends Day!" she wrote, along with the hashtag #NationalPetDay.
Bindi and Robert are very close. During her pregnancy, she posted a message on Instagram noting that he will be “the best uncle.” He is also ecstatic at having a niece and even drove their father’s truck to his first meeting with Grace.
Robert also walked Bindi down the aisle at her wedding last year.
“It was incredible. I think it was probably the most emotional I think I’ve ever been,” he told Australia's “Today” show.