Prince William has left King Edward VII hospital where Kate, the Duchess of Cambridge is being treated Hyperemesis gravidarum, a severe form morning sickness, earlier on Monday.
His departure was illuminated by thousands of camera flashes as the Prince got into a green Land Rover Discovery that was waiting outside the hospital, offering no comment to waiting journalists.
The shock pregnancy announcement caused a media storm and swarms of journalists, photographers and camera crews from around the world camped outside the hospital in spite of the cold weather.
Kate's illness brought forward the royal couple's announcement ahead of the 12-week mark, with Prince Harry, who is currently serving in Afghanistan told over email and the Queen also only informed today.
As the findings of the Leveson inquiry into press intrusion were debated in parliament, criticism of the large media presence were voiced by some politicians. Feelings of discomfort over the press hounding the Duchess could also be seen on Twitter.
Foreign Secretary William Hague suggested the newly announced pregnancy of the Duchess of Cambridge could be seen as a test of press restraint.
"Let's hope that she gets some privacy from the media as appropriate - without needing any new laws to tell the media to do that," he told ITV's The Agenda with Tom Bradby.
Kate is expected to remain in the hospital for a few days with St James Palace saying the Duchess will require a period of rest after she leaves.
Hyperemesis gravidarum can be serious but Kate was driven to the King Edward VII Hospital in a car and not an ambulance.
The Duchess made the journey from Bucklebury in Berkshire, where her parents Michael and Carole Middleton live, and it is thought she spent the weekend with them.
It was reported that the Queen's former gynaecologist Marcus Setchell, who delivered the Countess of Wessex's two children, is treating Kate at hospital.
Prince Phillip was the last royal to be treated at the King Edward VII's Hospital Sister Agnes, spending five days there during the Queen's Jubilee having treatment for a bladder infection.
The hospital, of which the Queen is a patron, has 58 en-suite, private, air conditioned rooms and has a long association with the royal family.
Grandfather to-be Prince Charles had a routine hernia operation there in 2003, while Camilla had a hysterectomy at the private hospital in 2008.
Sophie, the Countess of Wessex, was admitted to the hospital with an ectopic pregnancy in 2001. The late Queen Mother had two hip replacements performed by medical staff there and had a fish bone removed from her throat at the hospital in November 1982.