Blunt, 33, revealed in an interview with Entertainment Weekly that Andrews, 80, approved of her casting while speaking to Mary Poppins Returns director Rob Marshall.
"Rob said he was in the Hamptons, and he saw [Andrews], and he said, 'It's top secret, but Emily Blunt's playing Mary Poppins,'" Blunt related. "And she went, 'Oh, wonderful!'"
"I felt like I wanted to cry," the actress admitted. "It was lovely to get her stamp of approval. That took the edge off it, for sure."
Andrews starred as Mary Poppins in Disney's original 1964 adaptation of the P.L. Travers book series. Blunt will play the magical nanny in Mary Poppins Returns, which opens in theaters Dec. 25, 2018.
"I feel a little more trepidation with this [role] because she's so emblematic of people's nostalgia," the younger actress said. "It's such an important character in people's childhood."
"We're delving into the books a lot more, which is a different version of the character, I'll say that much," she revealed. "She's a little meaner, yeah."
Marshall said in a press release in May that he was looking forward "to creating an original movie musical." The movie will see Mary Poppins reunite with a grownup Jane and Michael Banks in Depression-era London.