The Duke of Edinburgh, Prince Philip, is likely to remain in hospital until next week, a royal source says, adding that doctors are acting out of an abundance of caution and the duke remains in good spirits.
Queen Elizabeth's 99-year-old husband was admitted to hospital on Tuesday as a precautionary measure after feeling ill with an ailment that is not related to COVID-19.
"Following consultation with his doctor the Duke of Edinburgh is likely to remain in hospital for observation and rest over the weekend and into next week," the source said.
"As we have said previously the doctor is acting with an abundance of caution. The Duke remains in good spirits."
Both Philip and the 94-year-old Queen received their first dose of the COVID-19 vaccine in January.
The Duke was admitted to the private King Edward VII's Hospital in central London after feeling unwell for a short period, Buckingham Palace said on Wednesday.
He spent four nights at the same hospital at the end of 2019 while being treated for a pre-existing condition.
Philip is now rarely seen in public.
He stepped down from official engagements in August 2017 after completing more than 22,000 solo events and thousands more alongside the Queen.
A former naval officer renowned for his sometimes brusque manner and humour, Philip married Elizabeth in 1947, five years before she became Queen.
He is now by far the longest-serving consort of any British monarch.