Prince Philip received bedside visits from the Queen and Prince Charles on Saturday as he recovered from heart surgery in hospital.
Buckingham Palace said 90-year-old Philip spent a "good night" at Papworth hospital in Cambridge, eastern England after he was rushed there from the Sandringham estate where the royals are spending Christmas.
The queen flew in by helicopter from Sandringham to the hospital 62 miles (100 kilometres) away accompanied by her youngest son, Prince Edward, the Press Association and the BBC reported.
An AFP photographer heard a helicopter land near the hospital and saw three Range Rover vehicles of the type used by the royal family entering the premises, before the chopper flew off again.
Prince Charles and Charles' wife Camilla later visited the hospital, the AFP photographer said.
Buckingham Palace said it would only confirm visits by members of the royal family after they had finished, but a spokeswoman had earlier confirmed that the royals would be coming to the hospital on Saturday.
"The Duke of Edinburgh had a good night," the palace spokeswoman told AFP.
British Prime Minister David Cameron's Downing Street office said he had been "kept informed of the situation and wishes the Duke of Edinburgh a very speedy recovery."
Greek-born Prince Philip is Britain's longest-serving consort, having married Elizabeth 64 years ago, and is well-known for his outspoken views and energy.
In a separate statement overnight, the palace said the prince "will remain in hospital under observation for a short period".
The health scare could mean he is confined to hospital over Christmas at a time when Prince William's wife Catherine is spending her first Christmas at the 60-acre (24-hectare) Sandringham estate as a member of the royal family.
The queen and her husband traditionally spend Christmas Day morning at St Mary Magdalene Church on the royal estate and greet well-wishers on their way to and from the service.
The Boxing Day shoot usually organised by Prince Philip could also be in doubt.
The palace said Philip had been taken for tests at the hospital after suffering chest pains while at Sandringham.
"The Duke of Edinburgh was found to have a blocked coronary artery which caused his chest pain. This was treated successfully by the minimally invasive procedure of coronary stenting," it said.
The procedure involves inserting a tube-like device called a stent into the blocked artery to open it up and help restore a healthy blood flow. It is often performed under local anaesthetic.
British media reported that emergency services were called to Sandringham at around 1800 GMT on Friday and Philip was flown by helicopter to the hospital.
Royal sources said the fact that family members were visiting was no indication that he was likely to stay in hospital any longer than expected, with one source saying that they would "obviously" want to see him on Christmas Eve.
Medical experts said many patients leave hospital only a day after having similar treatment.
"It does not require any major anaesthetic, this is all done when you re awake under local anaesthetic," cardiologist John Barton told the BBC.
"The recovery period is very rapid after this. Very often the people are discharged from the hospital within a day or two."
Papworth hospital specialises in cardiology and was where Britain's first heart transplant was carried out.
Philip joined his wife on an 11-day tour of Australia in October but has recently suffered occasional bouts of poor health and pulled out of a trip to Italy in October nursing a cold.
In 2012 the queen is due to mark her diamond jubilee celebrating 60 years on the British throne, but while other royals are scheduled to tour the globe next year, she and Philip are set to stay in Britain.