The former First Lady dazzled in her plunging frock, which featured a lacy V-neck trim and frills at the shoulders, to present the award for International Male Solo Artist to The Weeknd.
Appearing via video link from her home, Michelle wore her hair down in loose curls and added a glossy lip and subtle brown shadow to her eyes.
WATCH: Michelle Obama stuns for surprise appearance at the BRIT Awards
Addressing viewers at home, she said: "I am here because I am so so excited for this year's winner. He has made himself into one of the biggest names in music."
Michelle went on to praise The Weeknd and thanked him for donating millions to causes like COVID Relief and Black Lives Matter.
She continued: "He's made his impact not just on stage and in our earbuds, he's also donated millions to causes like COVID Relief and Black Lives Matter.
"He’s helped feed those displaced by violence in places like Ethiopia, he’s funded assistance to survivors of the explosion in Lebanon. So, let's just say in a tough year he's provided a light that's pretty blinding and given us all a reason to dance."
Michelle looked gorgeous in her black dress
Fans were shocked to see Michelle appear at the UK event, with many taking to social media to share their delight at seeing her on their TV screens.
"Michelle Obama has made my night. Just when you thought tonight couldn't get any better. They pull out Michelle Obama," one viewer posted on Twitter.
"The Weeknd delivered an amazing performance then got given his award by the Michelle Obama?!?! A legend of our time!!!" added another. A third said: "Oh my days!! Michelle Obama on Brits. I cannot believe my eyes."
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