Prince Philip will spend a second weekend in hospital and remain there "into next week" while receiving treatment for an infection, a royal source says.

The Queen's 99-year-old husband was admitted to central London's private King Edward VII Hospital on February 16 as a precautionary measure after feeling unwell.

Buckingham Palace has said the Duke of Edinburgh, who turns 100 on June 10, is comfortable and responding to treatment.

A senior palace source told the Mirror: “The Duke of Edinburgh will continue to stay in hospital over the weekend and into next week as he continues to receive treatment for an infection.

“He has been in good spirits and is comfortable.”

It is his longest ever hospital stay and the longest he has been apart from the Queen, 94, for nearly a year.

Prince Philip, 99, has been in hospital for 11 days (file photo)

The couple were isolating together at Windsor Castle during the Covid-19 pandemic.

Philip walked unaided into the private hospital when he was admitted on February 16.

He is being treated for an unspecified infection. It is not related to Covid-19.

In its latest statement, Buckingham Palace said on Tuesday: "He is comfortable and responding to treatment but is not expected to leave hospital for several days."

This is the longest Philip has spent in hospital since he had an exploratory operation on his abdomen in June 2013.

It will become his longest ever stay as an inpatient on Saturday.

The duke's youngest son, Prince Edward, 56, told Sky News on Tuesday that his father was getting better.

The Earl of Wessex added: "As far as I'm aware, he's a lot better ... so he's looking forward to getting out which is the most positive thing.

Keep up to date with all the latest news from the Queen, Charles, William, Kate, Harry, Meghan, George, Charlotte, Louis, Archie and the rest of the family.

We'll send the best Royal news directly to your inbox so you never have to miss a thing. Sign up to our newsletter here.

Edward said with a laugh that his father was "just a bit" frustrated at being in hospital.

He added: "You can only watch the clock so many times and the walls are only so interesting.

"We've had some lovely messages from all sorts of people and we really appreciate that and so does he, I've been passing them on."

Philip's oldest son, Prince Charles, 72, visited him in hospital for about 30 minutes last Saturday, appearing sombre as he left.

Keep up to date with all the latest news from the Queen, Charles, William, Kate, Harry, Meghan, George, Charlotte, Louis, Archie and the rest of the family.

We'll send the best Royal news directly to your inbox so you never have to miss a thing. Sign up to our newsletter here.

On Monday, grandson Prince Wiliam revealed that Philip is "OK" and hospital staff were "keeping an eye" on the great-grandfather.

The Queen and other Royal Family members have continued with their official duties while the duke has been in hospital.

She made a touching gesture to Philip by wearing a silver brooch from their engagement in her latest public appearance.

During a video call with health leaders delivering the Covid-19 vaccine, she called on the public to step up for their jab and issued a stern rebuke to anti-vaxxers.

In a subtle tribute to the Duke of Edinburgh, the monarch was seen wearing a brooch she first wore for their engagement 74 years ago.

The diamond clematis was first worn by Her Majesty in her official engagement photos with Prince Philip in July 1947.

Black and white images from the special occasion show the then-Princess Elizabeth wearing the six-petal brooch next to her future husband.

It's believed the brooch, which features six petals encrusted with diamonds and a single diamond in the centre of the piece, was a 21st birthday present from the Royal Household.

Prince Harry, meanwhile, revealed that Philip ends their Zoom calls not by pressing the 'hang up' button, but by closing his laptop when he's finished.

Harry, 36, told James Corden on The Late Late Show that he has been staying in touch with Philip and the Queen through video calls.

The Duke of Sussex, whose wife Meghan Markle is pregnant with their second child, added: "My grandfather, instead of pressing leave meeting, he just goes [signals closing a laptop].

"It's like 'bye' and as I'm pressing end to leave. It's like, 'okay, bye'."

Harry also revealed that the Queen and Philip sent great-grandson Archie, who turns two in May, a waffle maker in the post for Christmas.