Tom plays the beloved children's entertainer in the new film - a role for which he has bagged a Best Supporting Actor nomination at the Oscars - but Marielle reveals the performance was far from effortless for the star.
The filmmaker says she insisted he sing the theme to the show "Mister Rogers' Neighborhood" live, and that it took a huge number of takes to get right.
"We made him sing live, which you don't usually make movie stars do, but it's what Fred did so it's what we wanted to do," she tells The Guardian. "It was genuinely tricky. We did 22 takes, the most takes I think I've ever done of any scene in my life."
Although Tom is famously easygoing, he still had to rein in his natural enthusiasm to play the naturally relaxed and reassuring Rogers.
Explaining his process, Marielle adds,"It was almost like it was a martial art," explaining that the Forrest Gump star was "genuinely slowing his heart rate down, slowing his energy down" during his performance.