Britain's Anthony Joshua will defend his IBF and WBA heavyweight world titles against Bulgaria's Kubrat Pulev at Cardiff's Principality Stadium on 28 October.
The bout comes six months after Joshua stopped Wladimir Klitschko at Wembley Stadium in April, to add the WBA title to the IBF belt he claimed in 2016.
Pulev, 36, is the mandatory challenger for Joshua's IBF title.
"I have been eager to get back in the ring since Wembley," said Joshua, 27.
"I'll be locked away focusing on fight number 20 for the next eight weeks. I am excited to experience the atmosphere in a sold out Principality Stadium and aim to give the fans a spectacular night."
Klitschko delivered the only defeat of Pulev's 26-fight career in 2015 but the Bulgarian has since won five fights in a row, taking him to a position as the IBF's mandatory challenger.
"Anthony is a formidable opponent," said Pulev.
"We will not hug and hold, we will not run; we will stand and fight. His style fits mine perfectly and in boxing, styles make fights.
"My preparation will be very intense and I will be perfectly ready when I enter the ring so that he will have no chance to beat me."
Hearn has said that Joshua's aim is to face Pulev before meeting Cuban Luis Ortiz, the mandatory challenger for his WBA title - stressing that Joshua does not want to vacate either of his belts and would rather defend them before hopefully facing WBC title holder Deontay Wilder of the United States in the summer of 2018.
The heavyweight division's fourth recognised title is held by New Zealand's Joseph Parker, who defends the WBO belt against Briton Hughie Fury in Manchester on 23 September.
Joshua's meeting with Pulev is set to be the fourth night of boxing held at Wales' national stadium.
Matt Skelton overcame Danny Williams for the Commonwealth heavyweight title there in 2006, while Wales' Joe Calzaghe had two wins in front of his home crowd, against Peter Manfredo and Mikkel Kessler in 2007.