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By Kristen Torres

Emily Blunt tackled her fear of singing in front of crowds while on "Ellen" Monday — but not without the help of some famous backup singers.

The "Mary Poppins Returns" star agreed to perform after being surprised by famed boy-band the Backstreet Boys.

"Now I can do it, now I can do it," said Blunt, after hugging the band members.

The group broke out singing the chorus of "I Want It That Way," with Blunt taking on a small solo at the end. "You left me alone," Blunt said. "You weren't supposed to do that."

The impromptu musical moment came just after Blunt admitted she still gets anxious performing onstage.

Blunt is just one month away from making her debut as the new Mary Poppins — a role she was surprised to fill.

When director Rob Marshall called to offer her the coveted part, Blunt recalls "I knew there was a different energy behind this phone call. I mean, it was so charged and excited to tell me this news."

"I thought he's going to ask me to marry him," she joked. "This is where I get married to Rob Marshall."

But in lieu of a proposal, Blunt was offered the role of a lifetime.

"You didn't know anything about it before the call?" DeGeneres asked. "You didn't know someone was remaking Mary Poppins?"

"No. Nothing. It was completely new to me," Blunt replied.

"Mary Poppins Returns" hits theaters Dec. 19.