This move helped Boothroyd, 35, to become the Hornets manager last March where he has been hugely successful to date. "Kevin gave me a big step up the management ladder," says Boothroyd, whose third-placed side are just above Leeds in the Championship.
"I knew Kevin was looking for a first team coach so I arranged an interview and managed to talk my way in. He gave me the job and I will always be grateful to him. We parted on good terms. He said: 'good luck and I wish you well' and I'm looking forward to going up there again. I thoroughly enjoyed my time there. It was a huge learning curve for me and a big part of my life being around so many fantastic players.
"It's a wonderful club with some great people and I am pleased they are doing well. But we are going to try to win there because we really want to get to the Premiership. That's where I want to work."
Watford will be without former Leeds players Matthew Spring and Clarke Carlisle, who are ineligible to play against their old club tonight
He added: "I think it is going to be very hard, they are a very big club and we are the underdogs. We just have to go and do our best."