Casualty star Amanda Henderson had viewers in hysterics on the latest episode of Celebrity Mastermind with her answer to a question about climate activist Greta Thunberg.

Eastern Daily Press: Alix Dunmore as Siri, Kara-Lianne jones as Cinderella and Amanda Henderson as Alexa in Norwich Theatre Royal's Cinderella Credit: @richardjarmy - www.richardjarmy.co.ukAlix Dunmore as Siri, Kara-Lianne jones as Cinderella and Amanda Henderson as Alexa in Norwich Theatre Royal's Cinderella Credit: @richardjarmy - www.richardjarmy.co.uk (Image: smile@richardjarmy.co.uk)

Amanda, who is currently starring as Alexa the Ugly Sister in Norwich Theatre Royal's Cinderella, appeared on Celebrity Mastermind on Thursday night alongside Levi Roots, Geoff Norcott and Paul Chuckle.

The 33-year-old actress, who plays nurse Robyn Miller in Casualty, made a strong start on her specialist subject, which was songs from animated Disney films from 1989 to 1999 and scored eight points.

However, when it came to the general knowledge round, the pressure of the black chair left her stumped by one of the questions asked by presenter John Humphrys.

Eastern Daily Press: Greta Thunberg holds a climate change rally at the Greek Amphitheater in Denver, Colorado Picture: Anthony Quintano/FlickrGreta Thunberg holds a climate change rally at the Greek Amphitheater in Denver, Colorado Picture: Anthony Quintano/Flickr (Image: Anthony Quintano/Flickr)

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He asked her: "The 2019 book entitled No-one is Too Small To Make A Difference is a collection of speeches made by a Swedish climate change activist. What's her name?"

In a moment that is already being hailed one of the TV moments of the decade, Amanda's replied with "Sharon" and had a confused expression on her face.

The clip was shared on Twitter by comedian Mark Smith with the tweet "2020 is cancelled" and it has since had 1.7 million views and been retweeted almost 60,000 times.

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Author Magda Szubanski shared the tweet and wrote: "If you need a laugh watch this" and called it "comedy gold."

YouthStrike4Climate tweeted: "We want to thank Sharon for starting this incredible movement, you inspire us every day!"

Unfortunately, Amanda didn't manage to win the show, finishing in joint second place with Levi, after Paul came last, and it was won by Geoff with 13 points.

Celebrity Mastermind is available to watch on BBC iPlayer.