Robin Williams' final act of kindness on the set of his last film was the sweetest!

Los Angeles - Robin Williams helped a young co-star secure a prom date.

The late actor who was found hanged in August agreed to appear in a video for Skyler Gisondo along with their other Night at the Museum: Secret of the Tomb co-star Ben Stiller because the high school senior was away from home and unable to ask a girl out in the conventional way.

Skyler who plays Ben's son in the movie said: "All morning, Robin was pitching more ideas. He was saying 'Can I say this? Would it be appropriate to say this?' You're Robin Williams. You can say whatever you want!

''It turned into this three-minute, ridiculous thing. A prom-posal. I realised that was the most awesome three minutes of my life and I've accepted it will go downhill from there."

In the video, Robin makes a direct appeal on behalf of Skyler, saying: "Yo, Hillary, will you go to the prom with my man, Sky-ler?"

Ben then jokes: "He's a good guy, a great kisser. I don't know that personally, but I've seen. Just that time with the monkey. It was for a scene, but it seemed like you had a connection."

The gentle mocking is then interrupted by a monkey carrying a rose, prompting Robin to quip: "A monkey and a rose. That's so Freudian."

Skyler adored working with Robin on the film and will always treasure the "special" experience.

He told The Hollywood Reporter: "Robin was this bottomless reservoir of kindness and hilarity.

"It was just so special to work so closely with this guy who's movies I've grown up with and watch his preparedness and his kindness."

Check out the video here: