The 38-year-old entertainer stopped by The Ellen DeGeneres Show on Tuesday, where he revealed that it wasn't the intricate dance numbers or new music that gave him pause, rather it was one short, but complicated scene.
"You would think it's the incredibly elaborate dance numbers -- and that was hard -- but there's like one scene in this movie where I light a lamp, ride a bike, steal an apple from a cart, throw it to an orphan child all while singing in a Cockney accent," Miranda tells DeGeneres. "That moment is the hardest 10 seconds of my life. I'm sure there are takes of me just absolutely wacking poor orphan children. Just throwing apples too hard."
Despite the hilariously challenging nature of the scene, Miranda calls his role as Jack "one of the best jobs of my life." A big part of making the flick such a memorable experience was his co-star, Emily Blunt.
"She's absolutely perfect in this movie and it is not hard to pretend to be having fun with Mary Poppins on these amazing adventures," Miranda gushes of Blunt.
"Lin is just thrilling because he is one of the most positive people I have ever met and nothing is a step too far for him. That energy is quite infectious to be around and it's quite a big thing he has taken on, to not only take on a Cockney accent [but] surrounded by Cockney people in our crew. It's quite daunting," she said. "He has approached it with such confidence, and thrown himself into the dancing and singing, and I think it has been quite nice for him not to be having to write and produce and create every single word that is in a film, but just to be an actor. I think he loves that."
During the set visit, ET also caught up with Miranda, who revealed that he never had the "audacity" to dream that he'd get the chance to star in Mary Poppins.
"There are 'dream come true' moments -- getting your show on Broadway, getting to be in a movie -- and then there are dreams that you didn’t even have the audacity to have," Miranda said at the time. "Like, that there would be a sequel to Mary Poppins and you could be dancing with Mary Poppins someday. Who would have the audacity to have that dream?"
Watch the video below for more on Mary Poppins Returns, which hits theaters on Dec. 19: