Bindi Irwin has told her brother that he'll be the "best uncle" when she welcomes her baby girl next year.

Pregnant Bindi, 22, and Robert, 16, are the children of late dad and iconic conservationist Steve Irwin.

Now, sharing a snap of her embracing her baby brother, Bindi has penned a heartfelt tribute to the teen.

"Shoutout to my little brother (who definitely isn't 'little' anymore) for being such an incredible friend," the proud big sister wrote.

"You're always there for me and I know you will be the best uncle when our baby girl is born. Love you."

Bindi and hubby Chandler Powell announced in August that they were expecting, five months after they tied the knot at Australia Zoo.

Fans instantly went into meltdown at the news, telling Bindi that her late dad Steve would be proud of his daughter.

Their wedding ceremony featured tributes to Steve, who died in 2006 from a stingray attack while filming.

Robert got choked up on the big day as well, partly out of pride for his sister, and partly due to dad's absence.

And the couple have even shared a look at the first sonogram for their baby, who's expected in 2021.

Robert got choked up on his sister's wedding day about their late dad
They shared a look at the first sonogram

Bindi posted a snap of the two of them with a couple of zoo animals.

Chandler is clung onto by a koala while Bindi cradles a joey.

In her other hand, though, she's holding up a sonogram of "our human joey."

"The animal joeys we care for are excited to meet our human joey," the mum-to-be wrote.

"Baby Wildlife Warrior is about about the size of a hummingbird now!

"We can't wait to teach our little one about the importance of protecting our planet and the beauty of the wildlife and wild places we love so much.

"Thank you for your kindness and support on this magical journey."

They shared their baby joy after finding out they were expecting their first child together
Bindi has shared snaps of her dad, who sadly died in 2006

Bindi and Chandler held up a mini version of their own zoo uniform when they first dropped their pregnancy bombshell.

Bindi wrote: "Baby Wildlife Warrior due 2021.

Both Bindi and Robert are hugely proud of their dad
Bindi and Chandler were overjoyed with their baby news

"Chandler and I are proud to announce that we're expecting! It's an honour to share this special moment in our lives with you.

"Though I'm still in my first trimester, we really want you to be part of our journey from the beginning of this new life chapter.

"We couldn't wait to share the news as this beautiful little being has become the most important part of our lives.

"Your support means the world to us. Please let me know your best advice and send good vibes & prayers to our little sweetheart. Love & light."