“I live around the corner from him and he more or less looked at me and told me he was better than me at table tennis. So I got a table and said: ‘Come to mine and we’ll see who top dog is’."
Dore-based Brook was in the red corner and his opponent, wearing the blue colours with white stripes, was boxing fan and Sheffield Wednesday star Josh Windass.
The rest, as they say, is history, and consists of dinner dates, workouts and Netflix sessions (hold the chill).
Both men met through their nutritionist, Greg Marriott, and despite their club allegiances and rivalry on the table, have since struck up a friendship.
“He’s a good kid,” former world champion Brook, who boxed at his beloved Bramall Lane in 2017, tells The Star.
"As much as I’m United, I’m a big Sheffield man born and bred. I want the city to do well so I want both teams to do well.
"We might joke about, I dig him here and there with banter, but that’s about it.”
Windass established himself as a key player at Hillsborough in his first full season as a Sheffield Wednesday player last term and was the club’s top scorer with 10 goals in all competitions.
An injury sustained during pre-season has kept him on the sidelines in League One so far, but the 27-year-old – whose dad Dean represented both the Owls and the Blades – is finally closing in on a return to action.
"We have been going on the wattbike together and doing low-impact stuff on his knee,” adds 35-year-old Brook, who himself is back training at the Ingle Gym ahead of a possible long-awaited fight with rival Amir Khan.
"We have also been doing some recovery training together.
"He doesn’t want to leave, he’s always round the house. We are always watching some episode on Netflix, playing table tennis or going for lunch together.”
So, bromance aside, who boasts the bragging rights as top dog?
"You are only as good as your last fight,” says Brook. “The last time we played I annihilated him 3-0.
"I’m the king of table tennis.”
One suspects Windass Jnr may have a thing or two to say about that.