The Duke of Edinburgh is expected to remain in hospital for “observation and rest” into next week, sources have said.

Philip was admitted to King Edward VII’s hospital on Tuesday evening after feeling unwell and walked unaided into the medical centre.

The duke, who turns 100 on June 10, is in hospital for an undisclosed reason, although it is not coronavirus-related.

Sources told PA news agency: “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.

“As we have said previously the doctor is acting with an abundance of caution. The Duke remains in good spirits.”

There will be concern for the duke because of his age, but members of the monarchy have continued with royal duties this week.

The morning after he was admitted, the Prince of Wales and Duchess of Cornwall – who have received their Covid jabs – visited the Queen Elizabeth Hospital in Birmingham to learn about vaccination trials.

While on Thursday, the Queen carried out her first official in-person event of the year and made one of her most senior royal aides a Knight Commander of the Royal Victorian Order during a Windsor Castle ceremony.

Philip last had a spell in hospital when he spent four nights at the King Edward VII’s in December 2019, where he was treated for a “pre-existing condition” and discharged on Christmas Eve.

He has spent the lockdown with the Queen at Windsor Castle, where they have spent much of the past 12 months.