Anthony Mackie told the story on how Beyonce sang Halo to him. He shared the info on The Late, Late Show with James Corden. Mackie said he's seen Beyonce "many times."
Mackie continued, "So once I saw Beyoncé at Madison Square Garden, and around the stage she has this thing called the Beyhive, and I got Beyhive tickets. Beyoncé’s coming down the stairs, she's singing 'Halo' and she looks at me and she goes, 'halooo,' and I'm like 'oo-oo.'"
There's more - Mackie said, "And she reaches her hand out, and I hold her hand. And she looks at me and she sings like eight words, but it felt like 18 bars. And she was definitely holding my hand because she thought I was cute."
Beyonce's reaction to hearing Anthony Mackie and Judy Greer talking about being her best friend, is probably something like this.