Los Angeles, California - Bella Hadid has told fans she will be back to work "when I'm ready" after lengthy treatment for Lyme disease, scotching rumors she had stepped back from the catwalk for good.

The model has not appeared at some of the biggest events on the fashion calendar, including the Met Gala and Paris Fashion Week.

But in an Instagram post on Sunday, Hadid revealed "100+ days of Lyme, chronic disease, co-infection treatment, almost 15 years of invisible suffering."

Alongside numerous photos showing her receiving treatment, as well as of medical diagnoses – some dating back to childhood – the 26-year-old said her lengthy illness had been debilitating.

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"Living in this state, worsening with time and work while trying to make myself, my family and the people who support me, proud, had taken a toll on me in ways I can't really explain," she wrote.

But she assured the almost 60 million followers that she was on the mend.

"I am okay and you do not have to worry," she said, adding: "I'll be back when I'm ready."

The catwalk star, whose sister Gigi is also a model, said she was "finally healthy," and had grown as a person during the course of her treatment.

"Thank you to my genius Dr, and her INCREDIBLE team of nurses. I love you SO much!!!" she wrote.

"Thankful to my mommy for keeping all of my medical records, sticking by me, never leaving my side, protecting, supporting."

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Hadid said in April that root canal surgery had cased a flare-up of her Lyme disease, an illness humans can contract if bitten by a tick carrying the borrelia bacteria.

A bite from an infected tick causes fever, headache and tiredness. If untreated, the symptoms worsen to include immune system problems and joint stiffness, according to the Mayo Clinic.