Bindi Irwin commented that her baby daughter Grace Warrior has "the happiest face" in the sweet photo

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Robert Irwin is spending quality time with his baby niece.

The Crikey! It's the Irwins star, 17, shared a sweet photo Monday in which he smiles while holding sister Bindi Irwin's daughter Grace Warrior, 4 months. In the snapshot, Grace adorably beams for the camera as her doting uncle looks on.

"Hanging out with Grace in the camp after a big day catching crocs is the best 😊 She's lovin life up here on our crocodile research expedition!" Robert captioned the post. In the comment section, Bindi, 23, remarked, "The happiest face ❤️❤️❤️."

Robert Irwin with niece Grace
Credit: Robert Irwin/instagram

Bindi, who shares her baby with husband Chandler Powell, posted another pair of photos featuring Grace on Instagram Sunday, showing her baby girl getting to know nature. "Our beautiful angel is always ready for an adventure," the proud mom wrote.

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Robert told Entertainment Tonight in June about his efforts to become the "fun uncle" with Grace: "I'm already trying to teach her how to play the guitar. It's one of my passions, so she'll always go to sleep when I play the guitar. She loves it. I'm trying to be the fun Uncle Robert!"

He added to ET of baby Grace, "She's at that age now where she's really reacting to things, you know, when she sees a new animal. We met a koala for the first time the other day and her little face, she was all kinds of sleepy, and she saw that koala and her face just lit up. The biggest smile, and it was amazing. I can already tell she is a wildlife warrior. And I cannot wait to just introduce her to everything zoo life."

RELATED VIDEO: Bindi Irwin Shares Cute Video of Her Baby Girl Hanging with Tortoises: 'Little Wildlife Warrior'

Back in April, Robert wrote on Instagram, "Being Grace's uncle is awesome!! I can't wait to watch this little warrior grow up and take on the world - I reckon she'll be running the zoo in no time!"

"I feel so honoured that I'll get to share all the amazing experiences that I had growing up in a zoo, and teach her about everything from rescuing wildlife to caring for our family of animals!" he added.