Prince Philip, Queen Elizabeth's 99-year-old husband, was admitted to hospital on Tuesday evening as a precautionary measure with an ailment that is not Covid related.
"The Duke's admission is a precautionary measure, on the advice of His Royal Highness's Doctor, after feeling unwell. The Duke is expected to remain in hospital for a few days of observation and rest," the statement said.
The prince had been feeling unwell for a short period and he walked into hospital unaided, a royal source said. He does not have a Covid-19 related illness, the source added.
Queen Elizabeth and the prince have been staying at Windsor Castle, west of London, during Britain's coronavirus pandemic.
The queen remains at Windsor, the source said.
The prince, who stepped down from official engagements in August 2017, was previously admitted to hospital at the end of 2019.