The Queen met a face from her past when she celebrated the 70th anniversary of the United Nations body regulating global shipping - a former commander of the Royal Yacht Britannia.
Paddy McKnight, who was in charge of the famous vessel for two years, was among the International Maritime Organisation's (IMO) staff and other maritime officials from across the globe who met the monarch.
The Queen returned to the building - the only headquarters of a UN agency in London - 35 years after she officially opened the centre.
Mr McKnight, a former naval officer in his 70s who was in charge of Britannia from 1983-1985, said: "I'd been on the yacht 11 days before the Queen opened this building.
"I did a series of trips, the first one was a state visit to Sweden, as commander you're the CEO if something goes wrong you're the guy that carries the can. And the Queen is very sharp, she's very observant so things have got to be spot on."
The ex-naval officer, who was representing InterManager - the international trade association for the ship management industry, added while laughing: "There were no mishaps of which I was aware - it was one of those jobs if nobody said a thing, you were doing fine."
The Royal Yacht Britannia was taken out of service in 1997 and is now a popular tourist attraction based in Scotland.
During the Queen's visit to the IMO's headquarters on the southern bank of the River Thames overlooking the Houses of Parliament, the organisation's secretary-general Kitack Lim gave a speech highlighting the importance of freight carried by sea around the world.
He said: "Today we are celebrating 70 years of achievement in which the truly vital industry of shipping has become safer, cleaner and greener, thanks to the work of the IMO. We are also looking ahead to new challenges on the horizon.
"Billions of ordinary people all over the world rely on shipping every day of their lives - even if they don't realise it or understand it. It is our role to ensure shipping can continue to make this vital contribution to global wellbeing."
The IMO grew out of a need to standardise rules for all vessels and in 1948 it was established as the global standard-setting authority for the safety, security and environmental performance of international shipping.
During her visit the Queen was shown mementos of her previous visit, models of ships in the IMO's foyer and the huge three-sided lens from a Suffolk lighthouse.
Before leaving the Queen and secretary-general simultaneously cut a birthday cake and the monarch unveiled a plaque to mark her visit.