IBF champion Brook will put his belt on the line in front of a hometown crowd at Bramall Lane, against an unbeaten and very dangerous opponent.
Brook is back in England after a training camp in Fuerteventura and told Sky Sports News HQ that he is ready for action."It's fantastic to be home," said Brook. "It's a bit colder here but it's nice to be home, touch base, and see my kids.
"We are in fight week now so the days are flying past and it will soon be Saturday. I have had a really good camp, done a lot of cycling, drinking plenty of fluids.
"We have had really hard sparring, really good sparring, and I've done what's been asked of me, hitting all the targets. I couldn't be any happier at this moment."
Brook has to get back down to 147lbs after moving up to middleweight to unsuccessfully challenge Gennady Golovkin.
And Brook added: "I have been doing it properly. Greg Marriott, my nutritionist, he knows how I tick, he knows what I like, what I don't like, he knows how I work. He has been trying to keep me as happy as he can.
"The fact is, I have been looking at food differently. Not enjoying it, just looking at it to fuel me through my next workout.
"I have had to stay professional in this camp and be switched on throughout, but I have not been as moody as I thought I was going to be!
"I feel very good, I am very close to the weight, and 147 here we come!"
Brook is wary of exciting prospect Spence Jr and added: "I think he is a very, very good fighter. He is a young, hungry lion. He is challenging for the world title. I have been there, I know what it takes.
"I know what he is feeling and I also know what it is like to defend that world title, so I have seen both sides of the coin.
"Dominic (Ingle) has put me through it in training, I have had to dig in deep, and I am excited. I am ready for a war. I prepared for a war and I prepared for a fantastic fight.
"There are going to be two winners that night, myself and the fans. It is going to be one hell of a fight."
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