Groves and Eubank Jr will face off in the ring once again on Saturday night with millions of pounds, the WBA super-middleweight world title and a place in the World Boxing Super Series final on the line.
But they are familiar opponents to each other, having boxed as many as 50 times in training, according to coach Adam Booth.
Booth spent six years as Groves’ trainer and was in Eubank Jr’s corner for two fights in 2015.
George Groves was trained by Adam Booth for six years (GETTY)
And the legendary British coach believes Groves was the only man who ever gained the upper hand in the two fighters’ sessions together – although it was close.
“I don’t think either of them ever had better spars in terms of the work they got in,” Booth told Boxing News.
“They knew that if they made a mistake they would pay for it.
“There’s only one occasion I can recall when one of them was slightly hurt.
Chris Eubank Jr, Chris Eubank Sr and Adam Booth were all in one corner twice in 2015 (GETTY)
“That was, ironically, when George caught [Eubank] Junior with a left hook and Junior appeared to be stunned.
“There was definitely something that happened in that spar because of that left hook. That was probably one of the last spars they had.
“They did an average of six rounds each time and I’d guesstimate they did that on 30 different occasions. But it might be closer to 50.”
Eubank Jr is a slim 4/6 favourite with the bookies in the biggest fight of his career with a win setting him up with either Callum Smith or Jurgen Braehmer: they face off a week later in Germany for the other place in the WBSS final.
But many boxing fans and pundits have been left wondering whether Groves’ size – Eubank Jr is seen as a middleweight by some experts including Tony Bellew – will be too much for the 28-year-old to handle.
Eubank Jr meanwhile will hope to rely on his fitness and speed to blow Groves away.
“Either way, Booth believes neither man would have picked the other if the WBSS had not paired them,” Booth added.
“In terms of difficulty, Eubank Jr is tougher than anyone Groves has boxed.
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“If he can’t keep Eubank Jr on the end of that long jab, the fight is incredibly hard for Groves and Eubank Jr will be the hardest opponent he has fought.
“A lot depends on whether Groves can control the distance and whether he’s emotionally and technically competent enough when he can’t control the distance. But they are both wrong for each other.
“Eubank Jr is potentially going to be hit harder than he ever has been hit.
“I don’t think George will be hit harder than he ever has been hit, but, if he allows Eubank Jr to claim that space, he will certainly be hit more than he’s ever been hit.”