Jack and Jill made their debut just three weeks after they were born, 29th January 1976. They were twin silver tabbies, but were far from identical - Jack had striped markings, while Jill had spots.
Jack and Jill became known as Blue Peter's disappearing cats, for whenever they appeared on screen they tended to leap out of a presenter's lap.
A sequence of clips demonstrating the fact was put together by the production team, featuring various moments when the cats leapt out of sight. It was set to the theme of the cartoon Boss Cat, and was often requested by viewers as the clip they most wanted to see again.
On 15th May 1980 Jill gave birth to two kittens, and the happy family appeared on the show on 23rd June.
Sadly, Jill died of heart failure on 30th May 1983. Jack died suddenly on 20th April 1986.