The Welshman who, like Charlton, survived the Munich air disaster, passed away at the age of 73 after suffering a brain aneurism at the weekend.
"Well, I was very surprised because there was no warning really," Sir Bobby told MUTV. "But my immediate thought was what a smashing little lad he was - I still think of him as the little lad. When Sir Matt Busby started breaking up the older element and started introducing people like Kenny, it was a big step for him. He played really well and deserved his position on the field.
"He was fortunate in Munich but he will certainly be missed a lot. He was a very, very nice person and a good player - a tough, little player and fast.
"I'm really very sad because he was one of those very nice people you always like to see. Even up to a few months ago ,when I saw him last, he was always smiling. I'm very sorry it's happened."
The two former Busby Babes took to the field at the Liberty Stadium ahead of last season's 1-0 victory at Swansea.
"We went on the field together because he was born in Swansea," added Charlton. "He was a Welsh lad and very proud of being Welsh, I remember that most of all.
"When they asked the two of us if we'd go on the field to give the fans a wave, we were happy to do that. He was a really nice person and I was very, very sorry about him."