Costa posted a five-minute clip to his YouTube channel, titled "ROBIN Test Footage Scene," on Tuesday, showing a scene featuring himself as Williams and Sarah Murphree as Pam Dawber on the set of "Mork & Mindy."

The clip shows Dawber interrupting Williams as he runs through lines to break the news of comedian John Belushi's death -- and shows Williams' reaction to the news.

When Murphree tells Costa that Belushi had been found dead that morning, Costa finds it hard to digest the news, insisting: "No, I told you, I was with him.

John's not dead, I was with him last night."

"Blues Brothers" star Belushi died aged 33 of a cocaine and heroin overdose at the Chateau Marmont in Los Angeles in 1982.

After Murphree warns Costa: "I can't let what happened to him happen to you" and a knock on the door signals it is time for the pair to go back on set, Costa returns to reciting lines -- this time, with a break in his voice.

The short film left some viewers hankering for a full biopic of Williams, who died by suicide in 2014 after battling Lewy body dementia.

"Who else has been hoping Jamie would play Robin in a biopic since you saw his first Robin impressions?" one wrote.

"It's one thing to resemble a person but it's how much he sounds like him and has his mannerisms and expressions down that's so freaking impressive.