A famous portrait of Sir Winston Churchill, taken by photographer Yousuf Karsh, has been stolen from a hotel in Canada.

The photograph known as the "Roaring Lion" was taken soon after Churchill's address at the Canadian Parliament in December 1941. It had been at the Château Laurier hotel in Ottawa for over two decades before it was stolen.

The theft came to light after a staff member noticed that the frame in the Reading Lounge of the hotel was not hung properly. The frame also did not match the other portraits from the collection.

An inspection of the portrait later revealed that it was a fake one. The late photographer's estate confirmed that the "Karsh of Ottawa" signature was fake. It is, however, unclear when the original photograph first went missing from the hotel.

"I have seen that signature for 43 years. So, it took me just one second to know that someone had tried to copy it. It was a fake," Jerry Fielder who manages Karsh's estate, told The Guardian.

Ottawa police have launched an investigation into the matter. The hotel has also sought information from the public about the theft. Meanwhile, the other portraits from Karsh's collection at the hotel have been taken down so they can be secured properly.

"The hotel is incredibly proud to house this stunning Karsh collection, which was securely installed in 1998," the hotel's manager, Geneviève Dumas, said in a statement.

The artist had a long association with Château Laurier as the hotel hosted his first-ever exhibition in 1936. Karsh and his wife had lived in the hotel for almost 20 years. He had even gifted fifteen of his original works to the hotel.

According to the artist's website, he had waited in the Speaker's chamber after the "electrifying speech" to take a photograph.

Churchill told him that he could take just one photograph, and declined to put his cigar down. "Then I stepped toward him and, without premeditation, but ever so respectfully, I said, 'Forgive me, sir,' and plucked the cigar out of his mouth," Karsh recalled.

"By the time I got back to my camera, he looked so belligerent he could have devoured me. It was at that instant that I took the photograph," the website quotes Karsh as saying.

Winston Churchill: a life in pictures
5 April 1955: Winston Churchill, the Conservative prime minister, gives the V-sign as he leaves No 10 Downing Street for the last time Keystone/Getty Images