Adele told a group of fans she loved them as they sauntered through the capital singing her song after watching her take to the stage at Hyde Park.
The mum-of-one, 34, was on her way back from performing when she saw the gang belting out the lyrics to Someone Like You from her car.
Taking to Instagram on Monday night, Adele shared the sweet clip of her singing along with the fans, unnoticed from her vehicle, before gushing: "Ahhhh, love ya!"
The London-born singer made headlines on the weekend when she brought the house down with stunning renditions of her smash-hit tracks at the BTS gig.
She looked incredible sporting a floor length evening gown and regaled celebs including Tom Cruise and Cameron Diaz with her vocal range.
Adele's ex Simon Konecki and her boyfriend Rich Paul were also in attendance to support the star.
The gig had been sold out for months, but two lucky fans had a night money couldn't buy when they ended up with the best seats in the house.
And it was all thanks to an £8 flag they picked up at Holborn tube station.
One of Adele's team had spotted pals Jack Burns-Langton and Dean Barber in the crowd with the flag and asked if the singer could borrow it.
The next thing they knew they were given VIP All Access Passes plus drinks tokens.
Contacts manager Jack explained: "There was a guy waiting for us with our passes and they said 'get them a drink, make it a double, they're drinking on us tonight'".
But the best was yet to come for the friends.
"After she had done two songs she asked where Jack and Dean were," said their pal. "We erupted at that point. We got down to the front and security literally lifted us over the barrier.
"We were gobsmacked, we were just trying not to die on the spot. We could just hear everyone in VIP clapping."
Adele told the crowd what had happened with the flag, saying she wanted to give the pals "the best seats in the house".
The Easy on Me star then chatted to the pair, checking they were enjoying the hospitality and asking if they were drunk yet.
Dad-of-two Jack, 28, told The Mirror: "It was a pure fluke and there is no amount of money that could have bought us that experience - that's what made it even more surreal.
"It was the most unforgettable experience of my life. My wife said she thinks it tops our wedding day. You hear about these experiences from time to time but you just assume it's never going to happen to you."
