KARL'S WORST NIGHTMARE

Karl Stefanovic has opened up about his youngest daughter's "scary" ongoing health battle, one year after he rushed her to hospital with breathing difficulties.

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"Almost a year ago, my daughter Harper scared the living daylights out of us," the 48-year-old announced on Today.

"Struggling to breathe, we rushed her to the GP, then to hospital. There, we discovered the scary combination of letters we had never heard of before, RSV," he detailed. RSV stands for respiratory syncytial virus, an illness that, while common, can prove fatal for infants.