Bruce first brought Robertson from Scotland to the Tigers.
“When I signed him, he arrived at Hull with his mum and dad. I thought I had signed a schoolboy,” Bruce said on talkSPORT. “He was that young and that young-looking.
“In all honesty, at the start of his career, I didn’t really want to throw him in because he was young, but we had the first game of the season against QPR away in the Premier League, and we didn’t have a natural left-back.
“I am looking around and thinking, but I have just signed one, I am going to throw him in because he was just so young. He never came out of the team. That’s how well he had done.
“To follow his career now and what he has done for Liverpool is one of the great bits of management which you enjoy seeing the lads have a really great career.”