Big sister Bindi, 16, posted a sweet selfie on Instagram with her freckle-faced brother, captioning the pic, “This boy is my world.”
Bindi also wrote on Nov. 30, "Happy Birthday to my wonderful little brother. He is officially 11 years old today. He's one of my best friends and always manages to make me smile. He is more and more like Dad every day. I love him more than words and I'm so proud of the amazing human he is becoming."
Irwin died in 2006 after being fatally stabbed by a stingray.