The Duke of Edinburgh jokingly declared London Zoo's new Sumatran tiger enclosure "closed" moments after one of the big cats appeared inches from his legs.
Philip was surprised to see Jae Jae, a five-year-old male tiger, walk towards him - albeit behind safety glass - before he unveiled a plaque to commemorate his visit.
The royal was invited on Wednesday to open the £3.6 million attraction that will house the animal and his mate Melati, a four-year-old female.
Philip spoke after tiger keeper Teague Stubbington outlined the global threat to the animals and the work the zoo is doing to help conserve them.
As Sir Patrick Bateson, president of the Zoological Society of London which runs London Zoo, introduced the Duke, Jae Jae walked out into the enclosure behind them and Philip pointed at him to laughs from the invited audience.
In a short speech the royal said: "I used to be president of the zoo so it's marvellous all the work that's going on here and I also used to be president of the World Wildlife Fund which organised an 'operation tiger' years ago in India.
"So the problem with tigers is nothing new, it's just getting worse all over the place. But it's wonderful to see how much work is being done by the zoo. The last time I was here was to open a gorilla establishment - I hope they're alright and survive the winter.
"I can't help feeling somebody ought to knit jerseys for them or something."
To roars of laughter from the guests Philip ended with: "Anyway it gives me great pleasure to declare this place - well, closed actually."
Philip was taken on a tour of the new enclosure which opens to the public on Friday and which London Zoo believe will provide the perfect home for their two new big cats to breed in.
There are just 300 Sumatran tigers left in the wild and their habitat is being lost to the manufacture of palm oil.
The Duke saw the female tiger as he took the tour and she walked around a large pool before stopping to have a drink.
Tiger Territory is the name of the new attraction and it is the zoo's biggest investment since it created its Gorilla Kingdom enclosure in 2007.
The new home for the two big cats has been designed by the zoo's tiger keepers and conservationists to be the ultimate big-cat habitat.
Five times the size of the previous exhibit, with towering trees and a custom-built swimming pool, Jae Jae and Melati now have 2,500 square metres (27,00 sq ft) in which to roam.