The Queen got a good view of the BBC News Channel studio
The Queen has officially opened the BBC's rebuilt Broadcasting House, prompting laughter when she appeared behind the newsreaders live on TV.
That moment came as she toured the BBC newsroom, after earlier declaring the building open with a broadcast on BBC Radio 4, and also visiting BBC Radio 1.
The Queen said it was a "great pleasure" to declare the building open.
The Duke of Edinburgh had also been expected to attend, but was admitted to hospital on Thursday for an operation.
Crowds gathered outside the building, which flew the Royal Standard, to await the arrival of the Queen, who wore a powder blue coat and hat.
BBC Trust chairman Lord Patten and BBC director general Tony Hall met the Queen and escorted her on the first part of her visit.
She started the tour, her first visit to the corporation's recently expanded headquarters, by visiting BBC Radio 1 and meeting presenters including Nick Grimshaw, Trevor Nelson and Sara Cox.
She then visited the station's famous Live Lounge to watch a live performance by The Script, whose lead singer is Danny O'Donoghue, also well-known as a judge on BBC One show The Voice.
Her next destination was the building's third floor, where Fran Unsworth, the BBC's acting director of news, introduced her to several BBC Radio 4 staff, including Today presenter John Humphrys.
Background appearance She then joined another Today presenter, James Naughtie, and Sian Williams live on Radio 4 where she gave a short address to declare the BBC's new home open.
"I hope this new building will serve you well for the future and I am delighted to declare it open today," she said.
Afterwards, she met BBC newsreaders Huw Edwards and Sophie Raworth and weather presenter Carol Kirkwood at the start of a tour of the BBC newsroom.
The guided tour took her to look through the glass during a News Channel broadcast. Staff laughed and broke into a round of applause as she appeared in the background of the studio shot, prompting newreaders Julian Worricker and Sophie Long to turn round.
After leaving the basement-level newsroom, the Queen met stars including David Dimbleby and Strictly Come Dancing trio Sir Bruce Forsyth, Tess Daly and Claudia Winkleman in the ground-floor reception.
In the building's Media Cafe, which is normally open to the public but was closed for the duration of the visit, she was introduced to newsreader Fiona Bruce, Radio 1 DJ Greg James and actress Anne Reid.
At the end of her visit, the Queen unveiled a plaque marking the occasion at a reception attended by BBC staff, presenters and trustees.
Before the plaque was unveiled, Lord Patten wished the Duke of Edinburgh a quick recovery from his operation.
He said it was a "particular privilege" to welcome the Queen to Broadcasting House.
The Queen had previously visited Broadcasting House on five previous occasions but those were all before the BBC's extensive project to overhaul, modernise and expand the building to accommodate staff being moved from Television Centre, which closed in March.
The building is now home to nine radio networks, three 24-hour TV news channels, all of the BBC's main news bulletins and is the workplace for 6,000 BBC staff from the BBC's television, radio, news and online services.