Robert Irwin says it's vital we raise awareness of endometriosis after his sister's diagnosis.
Earlier this year, Bindi revealed that she had been dealing with the condition for the past decade.
The 24-year-old told her fans that she had struggle for a long time to get a proper diagnosis, and was told by doctors that she had to get on with it.
The illness sees tissue similar to the lining of the uterus grow outside the uterus, and can cause a huge amount of pain in a woman's pelvis, while also making it harder to become pregnant.
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And now, her brother has opened up about it, urging experts and society as a whole to take endometriosis more seriously.
"This is something we all need to talk about, it's a discussion we all need to have," he told Sunrise.
"Endometriosis, like so many women's health complications, affects more people than we realise.
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"She's now a new woman. I'm very vocal about women getting help and men putting it on their radar."
He went on: "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."
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In her post to Instagram back in March, Bindi explained that she had undergone surgery to remove 37 lesions and a cyst.
But she revealed that it had taken her too long to get the diagnosis she desperately needed.
Bindi wrote: "For 10yrs I’ve struggled with insurmountable fatigue, pain & nausea.
"A doctor told me it was simply something you deal with as a woman & I gave up entirely, trying to function through the pain.
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"I didn’t find answers until a friend @lesliemosier helped set me on a path of regaining my life.
"I decided to undergo surgery for endometriosis. Going in for surgery was scary but I knew I couldn’t live like I was. Every part of my life was getting torn apart because of the pain.
"To cut a long story short, they found 37 lesions, some very deep & difficult to remove, & a chocolate cyst. @seckinmd’s first words to me when I was in recovery were, 'How did you live with this much pain?'.
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"Validation for years of pain is indescribable."
The conservationist then added: "My family & friends who have been on this journey with me for 10+ yrs - THANK YOU, for encouraging me to find answers when I thought I’d never climb out. Thank you to the doctors & nurses who believed my pain.
"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. www.endofound.org."
Dominic Smithers