Ben Affleck has to ask audience over tricky Who Wants to Be a Millionaire McDonald's question

Ben Affleck had to ask the studio audience for help after a surprisingly tricky McDonald\s question left him scratching his head on Who Wants To Be A Millionaire.

The Argo actor, 53, put his trivia knowledge to the test on the latest celebrity edition of the US game show, where he teamed up with Jeopardy! champion Jamie Ding, in the hopes of winning up to $1 million for the Eastern Congo Initiative, founded by Affleck.

The duo breezed through the opening rounds before question 10 finally stopped them in their tracks.

Host Jimmy Kimmel asked: "Unless you specifically ask for more, which McDonald's sandwich is served with half a slice of cheese?"

The four possible burgers were the McCrispy, McRib, Filet-O-Fish, or Big Mac.

Affleck looked genuinely stumped, despite admitting he reckons he's more qualified than most to answer anything McDonald's-related.

Ben Affleck was stumped by a tough McDonald's question on Who Wants To Be A Millionnaire (Disney)

"I eat a lot of McDonald's - like a lot. All the time."

Even so, neither Affleck nor Ding, 35, were confident with an answer.

Rather than risking their impressive run, the pair decided to play it safe and use one of their lifelines, turning to the studio audience in the hopes they'd know their way around the Golden Arches menu better than he did.

The question stumped Affleck and his teammate (Gilbert Flores/Variety via Getty Images)

An audience-wide vote saw 'Filet-O-Fish' come out as the top answer, which sat right with the pair.

"I feel like that was sort of what I was going toward," said the Academy Award winner. "What about you?"

Ding, who has won 31 consecutive games of Jeopardy! replied: "Same. That was where I was going."

As it turns out, the Filet-O-Fish is the only standard McDonald's sandwich that comes with half a slice of American cheese by default, unless customers specifically ask for a full slice.

Emile Wamsteker/Bloomberg via Getty Images)

Locking in the audience answer helped Ding and Affleck keep the dream of winning $1 million alive.

Other contestants appearing on this star-studded season of the US Who Wants To Be A Millionaire include Jesse Eisenberg, Michael Keaton, Michael Che, Colin Jost, Awkwafina, Leslie Odom Jr, Jackie Tohn, Clayton Kershaw, and Brooks Nader.

The season kicked off with comedian Larry David and his daughter Cazzie David, who took home 32,000 for their chosen charity.

Viewers will have to tune in next week to see just how much money Affleck and Ding can raise - and whether there are any more fast food questions waiting around the corner.