The Queen visited Papworth Hospital earlier to visit Prince Philip after he underwent emergency heart surgery last night.
The Queen was brought in by Royal Helicopter and driven a short distance into Papworth Hospital to see the Duke of Edinburgh.
The 90 year-old Prince was also flown by helicopter from Sandringham yesterday after complaining of chest pains.
Buckingham Palace say the Duke has been successfully treated for a blocked coronary artery.
Last night, Philip was taken from Sandringham to the cardiothoracic unit at Papworth Hospital, between Cambridge and Huntingdon, last night, where an "invasive procedure of coronary stenting'' was performed.
The royal will remain in hospital for observation for a "short while".
Buckingham Palace said last night: "Following tests at Papworth Cardiothoracic Hospital in Cambridge this evening the Duke of Edinburgh was found to have a blocked coronary artery which caused his chest pains. This was treated successfully by the minimally invasive procedure of coronary stenting. Prince Philip will remain in hospital under observation for a short period.''
The Duke of Edinburgh has had a good night following his treatment for a blocked coronary artery, Buckingham Palace said in a further statement today.
The royal family were gathering at Sandringham when the Duke took ill - the Queen stayed for around 45 minutes, and was accompanied by the Earl of Wessex, the Duke of York and the Princess Royal.
They were met by Mr Stephen Bridge, chief executive of Papworth, and Professor John Cunningham, physician to the Queen. The Prince of Wales and Duchess of Cornwall also arrived by car 45 minutes later.'
Dr Simon Davies, consultant intervention cardiologist at the Royal Brompton Hospital in London, said Philip may have been on the verge of a heart attack or actually had one before the stenting procedure was performed.
Dr Davies said: "What they have done is they put a miniature sausage-shaped balloon down the artery, pushed the balloon into the narrowed section and then blown it up. That forces the material that is blocking the artery outwards and then gets the blood flowing down the artery again.
The stent is like a little metal sleeve fitted over the balloon when it is blown up. This metallic sleeve is opened up and then when the balloon is deflated and withdrawn the stent stays behind.''
Dr Davies added: "This is the most serious health scare suffered by the Duke who is known for being a robust and active 90 year-old. He has belied his years by carrying on with his many royal engagements and in October joined the Queen for an intensive 11-day tour of Australia that took the royal couple to many of the country's major cities."
The last time he was admitted to hospital for any length of time was in April 2008 when a chest infection laid him low for a number of days and he was eventually admitted for treatment.
But even with the respiratory problem he walked into the medical institution and walked out three days later and went on to make a full recovery.
The drama began when the Duke was rushed to hospital with reports saying he was flown to the medical institution.
Papworth describes itself as the UK's largest specialist cardiothoracic hospital and the country's main heart and lung transplant centre.
Following tests, the Duke was treated probably under local anaesthetic and the blockage was cleared successfully.
Well-wishers have been arriving at the hospital entrance through the morning to keep vigil. Braving the winter cold outside the hospital was Terry Hutt, 76, who had driven from Cambridge to wish the Duke a swift recovery.
The grandfather of three, a retired carpenter, has been an enthusiastic follower of the royals since he met the Queen Mother during the Blitz.
Today he brought Philip a gift to wish him a swift recovery. Mr Hutt said: "I've brought him a Father Christmas doll because I don't think he's a man of flowers. It's sad to have to come here for news but it's good news so far so I really hope he can come out to spend Christmas with his family, like everyone else.
Mr Hutt received treatment at Papworth three months ago and said he was sure the Duke was in good hands.
I had some trouble with my ticker and came here, it's a fantastic place.'' he said.
Schoolgirl Noor Khan, 14, also travelled over to the hospital from her home nearby in Caldecote. Noor said "My uncle lives here and called last night to say the Duke had arrived in Papworth. We got up this morning and came over because we want to wish him well. I really hope he gets better for Christmas.''