It was the first time the girls had come face-to-face since Buchanan was ousted from the group in 2009, the Daily Star Sunday reports.
Her departure - along with the previous exits of Mutya Buena and Siobhan Donaghy - meant that no original members of the group remained. The current lineup is Heidi Range, Amelle Berrabah and Jade Ewen.
Speaking of the reunion, Berrabah said: "It was a surreal moment. It is the first time we've seen each other since she left the band. It's so good to get closure on everything that's happened. She's looking really well and it's so nice we can chat again."
Range - who apparently cried at the meeting - added: "It was so nice to see her. It was sad not seeing her when we used to work so closely together. It was good to see she's doing well.
"I'm really glad we made up but that doesn't mean we'll start spending time together. We didn't socialise before, so nothing's changed there."
Sugababes recently signed a new three-album deal with Sony. Buchanan is working on solo material and will play her first gig at London's Jacques Townhouse on July 19.