Graham moves to the KC on-loan from Sunderland.
"For me, it's arguably the coup of the summer," Bruce told the Hull Daily Mail.
"When he became available on loan we felt it was a no-brainer. There's no secret that it hasn't quite worked out for him at Sunderland, sometimes that happens.
"But before that he had four years where he was terrific. He took the Championship by storm with Watford and then went on to Swansea where he did well again.
"Hopefully, a change of environment and a change of scenery will see him back to his best.
"He's a goalscorer and he's a finisher. When he gets in the positions, he usually scores. That's what we're hoping from him."