Their eagerly awaited unification bout takes place at the Principality Stadium, with the big-punching rivals also defending unbeaten records. Joshua is 20-0 and Parker 24-0.
The 28-year-old Joshua (WBA and IBF) is a huge fan favorite in Britain prompting 90,000 fans to flock to Wembley stadium to see his epic victory against Wladimir Klitschko in April. He survived the first knockdown of his career to stop the Ukrainian veteran in the 11th round. It was the biggest heavyweight fight in British history.
If Joshua beats the 26-year-old New Zealander (WBO), he will likely next take on unbeaten American Deontay Wilder (WBC) in a huge fight the boxing world desperately wants to see.
"These fights aren't easy because there is a lot on the line, so respect to team Parker for taking the challenge," Joshua said. "And you know me, I love this game. I am looking forward to it, training camp is underway and before you know it March 31 will be upon us."
The last undisputed heavyweight champion of the world was Lennox Lewis in 1999, and Joshua plans to emulate him.
But Parker pledged to end Joshua's unbeaten record in style - by putting him flat on the canvas.
"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?'" Parker said. "Well, now he's about to find out. And the world is about to find out whether AJ can really take a punch."
He clearly showed he could, against Klitschko, but he also struggled to hold off the much older Klitschko at times in that fight. Parker is a far younger and fresher opponent, and can also hit hard.
Joshua's promoter, Eddie Hearn, can barely contain his excitement.
"I'm delighted to get this fight made ... Champions should fight Champions and AJ continues to step up to the challenges," Hearn said. "It's the first time in history that two reigning heavyweight world champions have met in Britain. It's a classic match-up between two young, fast, undefeated belt holders and it's going to be an explosive fight."
Joshua beat Carlos Takam, stopping the 36-year-old Frenchman in the 10th round, at the same stadium in Cardiff back in October. Although some of his fans were not happy and jeered at the end, having fully expected Joshua to knock Takam out.
Parker's last fight was in England when he defended his WBO title for the second time, beating Britain's Hughie Fury on points in Manchester in September.
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