Mendes spoke to the media and confessed he was "terrified" of Grainge the first time they met.
"I had this crazy preconceived notion about what he was...," the singer said, "and what an executive like him was going to be like, act like."
"Luckily, none of that was true. And I learned so quickly how much he truly cared about music."
Richie also saluted his friend, adding, "It's hard enough to get a star as an artist... but to get a star as an executive... you got to be a magician. Congratulations, my friend. I know this is a proud moment for you and your family. I love you to death."
Bieber didn't speak, but he posed for photos with the man of the hour.