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.

Gisondo - 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 realized that was the most awesome three minutes of my life and I've accepted it will go downhill from there."

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

Stiller 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."

Gisondo adored working with Williams 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 whose movies I've grown up with and watch his preparedness and his kindness."