Caroline Wozniacki had just won her first Grand Slam at the Australian Open but despite achieving her dream, it turned to pain as she found out about having rheumatoid arthritis.

It is an incurable autoimmune disorder which causes stiff and painful joints and she just remembers being exhausted and being in pain.

“I looked at my husband David [Lee], and told him, ‘I literally can’t move, I’m so exhausted and in so much pain,” she told PEOPLE. “I felt like I’d been hit by a car and had mono at the same time.”

“It could have been cancer; it could have been a million things,” she continued. “Being a strong athlete and going from playing three hours on a tennis court and then the next day barely being able to get out of bed, raised a lot of question marks.”

“It was a big shock,” she said. “I’ve never had anyone in my family with RA or an immune disease — I just couldn’t understand how a fit young person could have this disease.”

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