"These fights aren't easy because there is a lot on the line, so respect to team Parker for taking the challenge".
Joshua aims to unify the heavyweight division in 2018 and win over Parker would see him claim the WBO belt - with only Deontay Wilder's WBC title left to win.
Parker believes he has been underestimated by the Londoner and has questioned Joshua's chin while threatening to give his rival a "huge shock".
Parker will fight Joshua at the Principality Stadium where he beat Carlos Takam in October 2017. My entire existence is now devoted to proving what the boxing world already knows'.More news: Mourinho not ruling out Man Utd move for 'phenomenal' Alexis
On April 29, Joshua defended his world title belt and won a vacant one when he stopped former longtime unified world champion Wladimir Klitschko in the 11th round of an all-time classic heavyweight title fight in which both fighters were knocked down and there was tremendous back-and-forth draw. "I think it's very important that Joe is very fast on his feet and very mobile in this fight against Joshua. And you know me, I love this game", he said.
"I've done it a few times now", he said. "Training camp is under way and before you know, 31 March will be upon us".
"We all know what happened last time I was in a unification fight".
The American, whose three-year reign as champion is the longest in the division, wants a fight with Joshua, calling the British Olympic gold medal victor out after beating Bermane Stiverne in November.More news: EPS for Canadian National Railway Company (CNI) Expected At $0.99
Parker's promoter David Higgins paid tribute to Hearn and Matchroom Boxing for the up-front way they had handled negotiations. "Being involved in a big fight is exciting - it's going to be a little part of history".
Parker (24-0) picked up the vacant WBO title with a points win over the previously unbeaten Andy Ruiz Jr.in Auckland in December of 2016.
"The stadium and Cardiff always come together to put on a fantastic show".
"Inside the stadium, boxing fans can expect yet another spectacular arena transformation, just days after the NatWest 6 Nations and ahead of Judgement Day VI and four nights of Ed Sheeran and more".More news: Citizenship and Immigration Services return to accepting DACA requests