The Queen has officially opened the new £2.5bn Terminal 2 building at Heathrow Airport in west London.
The terminal, known as the Queen's Terminal, replaces the very first passenger building which was opened by the Queen in 1955.
The Queen and the Duke of Edinburgh met people who were involved in the construction and staff working there.
Heathrow's new terminal was opened to passengers on 4 June, but the building will open in phases over six months.
United Airlines, Air Canada, ANA and Air China are using the terminal currently and eventually it will be home to 26 airlines and have 332 flights daily to 54 destinations.
The Queen also unveiled a commemorative plaque, which will later be installed in a public part of the building.
At the opening, Heathrow development director John Holland-Kaye said: "Our ambition to play our part to help Britain remain a global economic powerhouse by connecting all of Britain to global growth, that sense of duty is one for which we take inspiration from one of our most frequent flyers, Her Majesty the Queen."
Transport Secretary Patrick McLoughlin said: "This prestigious event marks the successful completion of one of the UK's largest construction projects.
"The new terminal is a perfect example of cutting-edge technology and design that can combine to make the best use of capacity, to improve the passengers' journey and experience, to boost the carbon efficiency by 40% over the previous building, and to produce stunning architecture that further reinforces Heathrow's reputation as a world class airport."
Following the official opening, the Queen and Duke boarded a flight to Northern Ireland for a three-day visit.
Terminal 2 is opened a day after there were severe problems with the baggage system at Terminal 1, which affected thousands of passengers and meant many passengers flew out without their bags.
'Severe baggage problems'
Following a problem with the automatic system on Sunday, it is believed up to 8,000 bags had to be processed manually. The airport said the system is now working normally.
A statement from Heathrow Airport said: "An IT issue with one of the sorters in the Terminal 1 baggage system yesterday caused some passengers to fly without their checked baggage.
"We are working with airlines to reunite passengers with their bags and we are sorry to those passengers who were affected."
Virgin Atlantic, which operates its domestic "Little Red" flights to Manchester, Edinburgh and Aberdeen from the terminal, were affected by what it said on Facebook were "severe baggage belt issues".
It also urged its passengers to "only travel with hand luggage, where possible".
Rachel Russell, who flew into Terminal 1 from Japan, wrote to the BBC and said: "I flew in from Japan with Virgin nearly 24 hours ago and had a connecting flight to Manchester.
"Although Virgin have been helpful, no one can tell me for definite where my bags are and when I will be reunited with them again."