Hearn said Takam, who hasn't fought since June, was on standby as soon as Joshua's bout against Pulev was announced.
Unified heavyweight world titleholder Anthony Joshua's defense against mandatory challenger Kubrat Pulev, scheduled for October 28 at Principality Stadium in Cardiff, Wales, is off but the card was salvaged when Carlos Takam stepped in on short notice on Monday.
Promoters Matchroom confirmed the IBF's third-ranked fighter Takam as replacement for Pulev on Monday.
Kubrat Pulev, who had one blemish on a 26-fight record, has been forced to pull out of the clash due to a shoulder injury that he suffered during a sparring session. Pulev, a former world title challenger, had always been eyeing this fight and had risen to become the mandatory challenger for the IBF belt.
As "AJ" had no choice in the matter to keep all his title belts, Hearn set up the Pulev fight with his friends over at Sauerland in order to begin 2018 with a clean slate for Joshua to choose from.
"When I called them this evening they were overjoyed and good to go".
"This hasn't happened in his career before but he is ready for all comers on 28 October".
Pulev has only lost once previously and that was to Klitschko so it was setting up to be an extremely intriguing fight, one that Joshua was favourite to win but he would have to be focused to make sure he did win it.
Any second opportunity for Pulev, whose only defeat came against Wladimir Klitschko in 2014, will therefore be significantly delayed. Takam (35-3-1, 27 KOs) has won two fights in a row since losing a competitive unanimous decision to Joseph Parker, who went on to win a heavyweight world title, in May 2016.