Bella Hadid used to cry over her mother's battle with Lyme disease.
The 19-year-old model is "so proud" of Yolanda Hadid for the way she has coped with the condition - which both she and her brother Anwar have also been diagnosed with - and admitted she has always felt frustrated that she couldn't do more to help.
She wrote on Instagram: "I am so proud of my mom. I have seen you in bed, struggling for the past five years of our lives, thinking to myself 'why would this happen to such an angel?
"I would cry to myself knowing that there was nothing I could do to help and that there were people going against you and what you are/were going through."
Bella recalled how she used to drive the 'Real Housewives of Beverly Hills' star to hospital in the early hours of the morning to receive treatment for the symptoms of the disease, which can affect the skin, joints, heart, and nervous system.
She added: "Incidents where you would be so sick, not being able to move your bones/body, and I would have to drive you to the hospital at 3 a.m. so I could see you get a shot of something just like every other day you would have to do treatment."
The stunning star ended her heartfelt post by urging other sufferers to buy Yolanda's new book, 'Believe Me: My Battle With the Invisible Disability of Lyme Disease'.
She wrote: "This book shows kids and adults with Lyme across the world that you are not alone and we believe you! I love you mommy."
Yolanda, who was diagnosed with the illness in 2012, previously credited Bella, Anwar, 16, and her oldest daughter Gigi, 19, for keeping her alive as she fought the disease.
She said: "My children [are] what kept me alive. I remember just waiting for them to get out of school, just to give them a hug and look at them for hope.
They're the ones that kept me fighting and wanting to live.
There were many days that I really didn't want to live anymore. But when you look at your children, it's not a choice anymore.
You have to get through, you have to keep fighting and searching to get well."
Yolanda, 52, also blamed the disease for the breakdown of her marriage to music producer David Foster, 66.
She explained: "At the end of the day, David never changed, I changed. Unfortunately, these are the cards that life dealt me.
It wasn't by choice.
But I'm not the woman I used to be and I probably will never be again.
My focus, my energy goes to trying to get well, trying to make a difference, trying to find a cure for my children ... and David's life is really travelling, going to concerts, loud music.
And I mean, I couldn't, I can barely listen to the radio."
Update your news preferences and get the latest news delivered to your inbox.