The daughter of fashion designer Tommy Hilfiger has revealed that her infamous (and false) line about him inventing cargo pants was down to her struggle with Lyme disease – and that at her lowest point, she served him a silver tray of her own poop.

Ally Hilfiger details how the debilitating disease – which was misdiagnosed for 14 of the 19 years she suffered from it – affected her life in her new book, Bite Me.

She attributes the idiotic quotes she became known for on her MTV reality show ‘Rich Girls’, which ran for just one season in 2003, to 'full-on Lyme brain,' according to Page Six.

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Tommy Hilfiger's daughter Ally (pictured together at the Global Lyme Alliance Gala in 2015) reveals that at her lowest point, she served her father her own poop on a silver tray

‘I had full-on Lyme brain and didn’t even know it,’ she writes. ‘I started to say things that I know were incorrect but couldn’t stop, like ‘My dad invented cargo pants.’

‘What? What the hell was I thinking?’

She also revealed that her frustration with her loved ones for not believing her despite her insistence that she was sick, led her to take drastic action with her father.

The 31-year-old says that, once, she called her father for help and he flew home for her.

But despite her knowing and insisting there was something physically wrong with her, she was frustrated that ‘no matter how hard I screamed, no one heard.’

‘I kept telling him I was sick,’ she writes. ‘He wasn’t getting the message.’

Ally (right with co-star Jaime Gleicher) also revealed that her undiagnosed Lyme disease was to blame for the dumb lines she came out with her on her short-lived reality TV show on MTV called 'Rich Girls'

She adds: ‘I got out of bed, grabbed a silver tray off the table, went into the bathroom, defecated on it, and handed it to him.

‘”You gotta get this tested,” I said.’

It was at this point, at the age of 18, that her father had her taken to Silver Hill Hospital for psychiatric care.

She explained that the combination of stress from her undiagnosed Lyme disease, her MTV reality show and her parents’ divorce led to her suffering a nervous breakdown.

Ally Hilfiger details how the debilitating disease affected her life in her new book, Bite Me

‘For about a month I started to unravel and it was basically a psychotic breakdown caused by the Lyme disease and the stress of the TV show and my parents divorcing,’ she told Page Six.

‘[My father] didn’t know what to do. I couldn’t even function. It was crazy. It was so intense.’

But it was only after she completed the hospital’s addiction recovery program that she met Dr Ellyn Shander, who finally correctly diagnosed her Lyme disease.

Ally is understood to have contracted the illness, which is carried and spread by ticks, when she was seven – but she has said she wasn’t diagnosed until the age of 21.

In an interview with the Daily Mail last year, she said the illness had transformed her young body into that of an ’80-year-old woman.’

'I couldn't put lotion on my legs because it felt as if I was being beaten with a baseball bat,’ she said. ‘I was like an 80-year-old woman.

'It had taken over every single cell in my body and in my brain.'

Undiagnosed, the fashion heiress suffered the disease's crippling symptoms, including chronic fatigue, headaches, memory loss and joint pain, for almost two decades.

She described the pain as 'excruciating', detailing how it would often leave her sitting in the bath for hours or walking with a stick.

After recovering from the illness, which is best treated if discovered early, Ally gave birth to a healthy daughter in 2014.

Speaking after being cured, she said: 'The only thing that kept me going was the hope that I would possibly one day become a mother.

'Today, I am proud to stand here and tell you I'm finally cured.'