Oprah Surprises Beyonce at Her Big Premiere!

Though it's pretty much impossible to upstage Beyonce, one star ended up almost stealing the show at Beyonce's New York City premiere of her new HBO documentary Life Is But A Dream -- Oprah!

Oprah, who interviewed Beyonce for her show Oprah's Next Chapter, caused chaos on the red carpet due to her surprise appearance, and teased her upcoming rare interview with one of the most notoriously private stars in the business.

Pics: Beyonce Gets Candid and Personal

"That's what we can't believe -- how she opened herself up," Oprah told ET about her big Beyonce interview. "She just said, 'I'm gonna let it go,' and let it out there."

And the most surprising thing about her interview?

"That she was equally as open in the interview as she was with the film."

Video: Beyonce Unveils Blue Ivy's Ultrasound

Oprah's BFF Gayle King also revealed that she sat in on the two superstars' meeting.

"It was amazing," she said. "When you see the documentary, it's a side of Beyonce you haven't seen before --but the conversation between Oprah and Beyonce is also something you've never seen before."

Check out the video to see Beyonce's stunning Elie Saab Couture gown, and The Dream getting candid about his much talked-about "swap meet" Grammy moment with Jay-Z.

Life Is But A Dream airs February 16 on HBO at 9 p.m., and Beyonce's interview with Oprah also airs on February 16 at 8 p.m. on OWN.