Model Bella Hadid is secretly battling Lyme disease.

The catwalk star and her younger brother Anwar have been struggling with the condition for several years, according to their mother, model-turned-TV star Yolanda Foster.

She confirmed the news as she picked up an award at the Global Lyme Alliance Gala in New York City on Thursday (08Oct15) while talking about her own battle with the tick-borne illness.

"When my two youngest children, Bella and Anwar, were diagnosed with chronic Lyme disease in early 2012, watching my babies struggle in silence in order to support me in my journey struck the deepest core of hopelessness inside of me," Yolanda told the audience.

"This award is for Anwar and Bella. This is my token and my promise to you that I will not allow you to live a life of pain and suffering. I will walk to the end of the earth to find a cure so that you can live a healthy life that you deserve. No child should suffer the way that you do... I thank you both for your extraordinary selflessness during this journey. Your unwavering love and compassion has kept me alive and fighting through the darkest days of my life."

The news comes just months after Bella received treatment for a mystery illness. She was admitted to hospital in July (15), but did not tell fans details of her illness.