Kate Middleton suffered a setback in her recovery from severe pregnancy sickness when her condition deteriorated yesterday.
Ms Middleton, who spent three nights in hospital last week being treated for hyperemesis gravidarum, took a turn for the worse as she spent the weekend at Kensington Palace.
Prince William pulled out of a planned official engagement at the British Military Tournament at Earl's Court, London, last night, so he could look after his wife.
Kate (30) had said she was feeling "much better" when she was discharged from hospital on Thursday morning.
But at lunchtime yesterday, St James's Palace announced William would be "spending Sunday privately with the duchess" instead of going to Earl's Court.
Kate's condition was not serious enough for her doctors to consider sending her back to hospital.
When he attended a charity tennis gala on Saturday night, Prince William had spoken about his wife's condition for the first time.
He told a guest: "I don't know why they call it morning sickness – they should call it all-day and all-night sickness. It's a long old process but she is getting there. She feels like it is going to go on forever."