After playing alongside his brother Prince Harry, he said of his son at a presentation ceremony: "He likes to move around a lot, he wriggles a lot, he keeps us on our toes."
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Dr Michio Hirano denied having any financial interest in the experimental treatment considered for the baby.
The measures are set to be included in a court-mandated clean air strategy the Government is due to publish on Wednesday.
Low pressure in the Atlantic brings a spell of wet and windy weather on Wednesday.