Conor Benn's fight against Chris Eubank Jr in London this weekend has been "formally" postponed after Benn tested positive for a banned substance, co-promoters Matchroom and Wasserman Boxing said on Thursday.
Promoters Eddie Hearn and Kalle Sauerland conceded defeat in their attempts to stage the catchweight meeting at the O2 arena after the British Boxing Board of Control declared it was "prohibited" and "not in the interests of boxing".
The BBBofC issued a statement on Wednesday after it was revealed that trace amounts of the fertility drug clomiphene, which elevates testosterone levels in men, had shown up in a recent test by the Voluntary Anti-Doping Association (VADA).
"After discussions with various parties, we have taken the decision to formally postpone the bout between Chris Eubank Jr and Conor Benn," said a statement from both promoters on Thursday.
"It is undeniable that the British Boxing Board of Control's decision to withdraw their sanctioning was procedurally flawed and without due process. That remains a legal issue between the promoters and the board which we intend to pursue.
"However, whilst there are legal routes to facilitate the fight taking place as planned, we do not believe that it is in the fighters' interests for those to be pursued at such a late stage, or in the wider interests of the sport.
"As promoters, we take our obligations and duties very seriously, and a full investigation will now need to take place."
Earlier Thursday, Hearn, who works as Benn's promoter, used social media to rule out appointing an overseas governing body to sanction the fight.
The bout was billed as a continuation of the Benn v Eubank feud that saw the rivals' fathers battle it out in two ferocious contests in the early 1990s.
A catchweight of 157 pounds (71 kilograms) was agreed for the sons to continue the family feud into a trilogy fight, meaning Benn, 26, would have had to move up two weight divisions and Eubank Jr lose three pounds.
Responding to the fight postponement, Eubank Jr, 33, tweeted: "Conor got caught using an illegal substance so the fight is off. Can't believe it.
"I really apologise to the fans and everyone that bought tickets, travelled and booked hotels, this should not of happened. He has escaped his schooling...for now."