Robert Irwin passionately discussed the importance of raising awareness of endometriosis after his sister Bindi's decade-long battle with it.
Bindi, 24, was in "insurmountable pain" for the last decade due to the disease, which sees tissue similar to the uterus lining growing outside the uterus.
It can cause severe pain in the pelvis and make it harder to get pregnant.
Two months ago, Bindi underwent surgery, which found 37 lesions and a cyst, after years of pain, fatigue and nausea.
Doctors previously told her that "it was simply something you deal with as a woman", resulting in her giving up.
And now, her brother Robert discussed her condition during a chat on Sunrise on Monday.
"This is something we all need to talk about, it's a discussion we all need to have. Endometriosis, like so many women's health complications, affects more people than we realise," he explained to hosts David Koch and Natalie Barr.
"She's now a new woman. I'm very vocal about women getting help and men putting it on their radar."
He added: "So many women go undiagnosed and live through hellish conditions.
"Bindi was going downhill fast and since getting treatment after being turned down and completely written off, being told 'it's all in your head', 'it's normal', she finally got the help she needed and deserved and she's a new woman."
In March, Bindi took to her Instagram page to share a photo of herself smiling from her hospital bed after undergoing surgery.
She said that going into the surgery was "scary" but it was something she wanted to do as she "couldn't live like I was".
"Every part of my life was getting torn apart because of the pain," Bindi added. "To cut a long story short, they found 37 lesions, some very deep & difficult to remove, & a chocolate cyst."
Her doctor asked her how she lived through the pain for so many years and she thanked those around her for supporting her.
The star concluded: "I’m aware of millions of women struggling with a similar story. There’s stigma around this awful disease. I’m sharing my story for anyone who reads this & is quietly dealing with pain & no answers. Let this be your validation that your pain is real & you deserve help. Keep searching for answers."
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