The 16-year-old shared a sweet selfie with younger brother Robert on Instagram

By Anya Leon
Updated January 04, 2015 02:35 PM
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Courtesy Bindi Irwin

Wildlife isn’t the only thing that has captured Bindi Irwin‘s heart.

The daughter of the late Steve Irwin played the role of proud big sister when she snapped a sweet selfie with her younger brother, 11-year-old Robert, on Saturday.

“This boy is my world,” Bindi, 16, captioned the shot of the siblings smiling for the camera, adding a heart emoji at the end.

It’s been a good year for Bindi – who also showed off her new darker do in the photo – as she celebrated her 16th birthday with a trip to get her learner’s permit.

But the actress told PEOPLE in July that the transition since the Crocodile Hunter‘s death in 2006 continues to be difficult.

“That kind of sadness never goes away. It’s like losing a piece of your heart that you never get back,” she said.