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Promoters Matchroom Boxing have confirmed that IBF and WBA title-holder Joshua will go head-to-head with New Zealander Parker, the WBO champion, concluding weeks of fractious negotiations between the two sides.
The mega bout will be held at Cardiff's Principality Stadium, the location for Joshua’s win over Carlos Takam in his last fight.
Joshua said: "I would like to announce the official news that myself and Joseph Parker will be fighting on March 31 at Principality Stadium in Cardiff.
"It is a unification heavyweight championship fight. We all know what happened last time I was in a unification heavyweight championship fight - it was gruelling, it was interesting and we both left the ring with masses of respect
Anthony Joshua's career defining moments
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“Anthony Joshua v Joseph Parker fight CONFIRMED: Date and location set for unification bout”
Anthony Joshua v Joseph Parker fight CONFIRMED: Date and location set for unification bout
"These fights aren't easy because there is a lot on the line, so respect to team Parker for taking the challenge.
“I am looking forward to it, training camp is under way and before you know it March 31 will be upon us."
Joshua unified the IBF and WBA titles with his famous win over Wladimir Klitschko last April, before then battling out a late stoppage win over Takam in October.
The Parker, 26, made his UK debut one month before, when he earned an underwhelming points win over Hughie Fury at the Manchester Arena.
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Parker said: "Anthony Joshua is in for a huge shock.
“A couple of months ago I heard him say 'why should I be worried about this little kid from New Zealand'?
"Well, now he's about to find out. And the world is about to find out whether AJ can really take a punch.
“My entire existence is now devoted to proving what the boxing world already knows."