The son of comedian Eric Morecambe has said how "fantastic" it was to find a missing episode of the Morecambe and Wise Show in the family home's attic.
Dating from 1970, the tape of the show had been wiped by the BBC so the expensive tape could be re-used.
Gary Morecambe, 65, said he was hunting round in the attic when he found film in a canister.
"It's a huge discovery because it was presumed missing and lost for good," he said.
"That it crops up is fantastic."
Morecambe and Wise fronted 175 shows over a 22-year television career and in their 1970s heyday regularly pulled in more than 20 million viewers every week, with the duo's Christmas show seen as a "must-watch" by British viewers.
While looking for paperwork, Morecambe's son found the unlabelled film can at the family home in Harpenden, Hertfordshire.
"I was looking through other stuff. As the decades go by we hadn't really sorted enough out and my mother said why don't you have a look in the attic," said Gary.
"I got in there and came across five large canisters with spools in them.
"Four of them were blank or damaged, but the other one had a BBC stamp on it."
The film was checked by experts and the episode turned out to be their first show made for BBC One, dating from 8 October 1970 after they moved from BBC Two.
Morecambe and Wise on the BBC
The Morecambe and Wise Show first ran on BBC Two on 2 September 1968. It marked the duo's return after 13 years away, during which time they had found success at ITV.
The BBC used the show to push its relatively-new colour television service, making them Radio Times cover stars.
Eric and Ernie became the nation's most popular double act and their show became unmissable television, culminating in the 1977 Christmas Day special, which was watched by 28 million viewers.
Gary Morecambe, who now lives in Ernie Wise's home city of Leeds, said Eric would always watch the Christmas specials with his family.
"[Eric] would never stop laughing. He loved watching the show. And at the end he'd stand up and say 'I thought Ernie was really good'."
The pair returned to ITV at the end of their career for a show that ran between 1978 and 1983.
Eric Morecambe died in 1984 and Ernie Wise in 1999.
Gary Morecambe said the episode was one from their earliest days of working with writer Eddie Braben, who went on to pen most of their most famous sketches.
"There is a lot in the show that will be incredibly familiar to people, showing the Eric and Ernie we came to know and love," he said.
Viewers had the opportunity to view the slice of classic comedy once again on ITV at 21:00 BST.
The ITV show also included rare archive film of the duo at work.
The duo's long-time collaborator, Ann Hamilton, played a nurse in a hospital sketch, looking on as Eric ate all of Ernie's grapes and then used the empty bag to catch an invisible ball.
The programme also featured celebrity Morecambe and Wise fans including actor Toby Jones, talk show host Jonathan Ross and comedians Ben Miller and Eddie Izzard.