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Luckily for those who live nearby, it turned out to be someone's expensive pet - a Savannah cat - that had broken out of a property not too far way.
The cat has been pictured near to some of the incredibly lavish houses in the leafy part of Hampstead nicknamed 'Billionaires Row'.
One of the pictures, taken by a resident of the North London neighbourhood, showed the animal standing around on its haunches, as if ready to spring at something.
Police were joined at the scene by animal experts, but between them they were unable to capture the animal.
Armed police were called out, but have since been told that they're not needed.
A spokesperson for the Metropolitan Police said: "Police were called at approximately 21:00hrs on Monday, 25 May to reports of a large cat seen in a garden in Winnington Road, N2.
"Officers attended the scene.
"An animal expert also attended and visually assessed the cat; it was concluded the animal was not thought to be dangerous or a threat to the public.
"The cat made off from the garden; enquiries continue to locate it.
"There have been no reports of attacks or injuries to members of public."
Despite the fact that we now know that it was just somebody's expensive pet, you can understand why the residents would have been a bit fearful of approaching it.
It's a big cat, after all. Not many folks will have heard of a Savannah cat before.
One said: "I was sitting having dinner with my daughter in the garden when the head appeared. It looked normal so I didn't take much notice but then the body came out.
"It was elongated, really too big for a domestic pet. The markings were like that of a cheetah or leopard."
"We were scared. I said to myself 'we should not be here' and ran in the house. I took a picture on the way, it was a frightening.
"We called the police and armed officers started the hunt for the animal. They told us to stay inside. There were two police helicopters overhead. It was very dramatic, I can understand it. At that stage they had to think it was a dangerous wildcat."
The Savannah cat is a hybrid between a serval - a type of African wild cat - and an ordinary domestic cat.
It is the largest of all domestic cat breeds, with the male cats being larger than the females. They've got a distinctive spotted coat, much like the cat in the picture.
They are very expensive, so you'd have to live somewhere like Hampstead to own one, but they're not a threat to the public.
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