Eddie Murphy was to play Bill Cosby on Saturday Night Live, tweets Norm Macdonald

Canadian expat Norm Macdonald pulled the curtains from Saturday Night Live's anniversary show on Wednesday, in one of his signature long form stories on Twitter.

The Ottawa-born Macdonald talked about working with producer Lorne Michaels and the rest of the cast on the sketches to be performed on the show's historic 40th anniversary show.

The biggest revelation was surely the original plan for Celebrity Jeopardy, where former SNL mainstay Eddie Murphy would play embattled comedian Bill Cosby.

In the segment, says Macdonald, Murphy would appear in a short video clip for a question with the category "potent potables" as Cosby, dressed in a signature multicoloured sweater, mixing a drink. Cosby's name has been synonymous with controversy in the past year, as several women have laid allegations of sexual assault on the comedian and actor.

Murphy decided against playing the role at the last minute. Current SNL cast member Kenan Thompson instead played the role of Cosby.

Regardless, Macdonald had glowing praise for Murphy's work on the show, both past and present.

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He also discussed the genesis of Celebrity Jeopardy, saying that he lifted it almost wholesale from the SCTV skit Half-Wits. Macdonald asked Martin Short for permission to use the idea, which eventually turned into one of Saturday Night Live's most famous skits, featuring Will Farrell as a constantly exasperated Alex Trebek.

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Can't read this tweet? Click here.

Macdonald also wrote that while Murphy was an SNL cast member in the 1980s, "in Lorne's absence, (he) kept the show alive. Singlehandedly."

"To every comedian who ever performed on SNL, what Eddie accomplished was unthinkable."

Macdonald spent five seasons with SNL, and anchored the "Weekend Update" segment for three years.

You can read all of Macdonald's tweets in chronological order here, and check out his Twitter account here.