LONDON -- Prince Philip, the 99-year-old husband of Queen Elizabeth II who is beginning a third week in hospital, is "slightly improving" although it "hurts at moments," Camilla, the Duchess of Cornwall said on Wednesday.

Philip, the Duke of Edinburgh, was admitted to hospital on Feb. 16 after he felt unwell to receive treatment for an unspecified, but not COVID-19-related, infection.

On Monday, he was transferred to another hospital which specializes in cardiac treatment for additional tests and observation relating a pre-existing heart condition, Buckingham Palace said.

On a tour of a vaccination center in south London, Camilla, the wife of heir-to-the-throne Prince Charles, told a volunteer the duke was "slightly improving" but it "hurts at moments."

"We keep our fingers crossed," Camilla told the volunteer at the center in Croydon.

Greek-born Philip, who turns 100 in June, has required hospital treatment a number of times in the last decade for a recurrence of a bladder infection. At Christmas in 2011 he had an operation to clear a blocked artery in his heart after being rushed to hospital with chest pains.

His current stay is the longest he has required hospital treatment, although Buckingham Palace has said he is comfortable and in good spirits.

The Queen, 94, has remained at Windsor Castle, west of London, where the couple have been staying during the coronavirus lockdown, and has continued to carry out her official duties, albeit remotely.

Both she and Philip have received their first COVID-19 vaccine dose as part of Britain's mass vaccination rollout.