“Get Ur Freak On” rapper Missy Elliott says she was a little freaked out shooting the viral-hit “Carpool Karaoke” video with Michelle Obama, but that the first lady put her at ease.

“When we got in the car and I saw her rapping ‘Get Ur Freak On,’ it kind of bugged me out!” Elliott, 45, tells People magazine about the segment that ran early Thursday morning on CBS’ “The Late Late Show with James Corden” and racked up nearly one million YouTube views in fewer than 24 hours. “I know for a fact that it was all over my face like, ‘Wait, is she rapping this?’ But that goes to show you just how cool she is. People hold her in such a high regard — as you should — but she’s so down to earth. I was just sitting in the back like, ‘I gotta be dreaming. This ain’t even real. Is somebody going to wake me up and say, ‘You overslept.’ ”

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Elliott confesses, “I was probably more nervous about forgetting my words,” saying she was concerned that, “I’d start mixing ‘Work It’ with ‘The Rain’ with ‘Get Ur Freak On.’ But I wasn’t nervous about being in the car because they made me feel like they knew me.”

The rapper, who suddenly appears in the back seat about 10 minutes into the nearly 15-minute video of Corden, 37, driving Obama, 52, around the White House grounds, sings along to both her own song and to “This Is For My Girls,” the Diane Warren-penned benefit song for the first lady’s Let Girls Learn educational initiative.

“I wanted to be in support of Let Girls Learn so girls across the world could have education to become leaders and great mothers,” Elliott says. “I don’t want my legacy to just be about music that I’ve done. I want it to be about great causes like this.”

Earlier in the segment, Obama and Corden sing along to Stevie Wonder’s “Signed, Sealed, Delivered I’m Yours” and Beyoncé’s “Single Ladies (Put a Ring on It).”

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“It’s one thing when you’re watching on TV … but she’s so down to earth,” Elliott says of Obama. “She’s like one of my aunts that would be at a cook-out. She’s so cool you almost forget! You almost gotta remind yourself, ‘Hold up, this is the first lady. You ain’t at the family reunion!’ ”