Anthony Joshua seeking third heavyweight belt in March 31 fight against Joseph Parker

Anthony Joshua, moving toward the possibility of becoming the first unified heavyweight champion since countryman Lennox Lewis, agreed on Sunday to fight Joseph Parker on March 31 in Cardiff, Wales.

The bout, at Principality Stadium, will have Joshua’s World Boxing Assn. and International Boxing Federation belts on the line, along with the World Boxing Organization belt of New Zealand’s Parker (24-0).

England’s Joshua (20-0, 20 knockouts) won the WBA belt by virtue of his stirring 11th-round technical knockout of former long-reigning heavyweight champion Wladimir Klitschko in front of 90,000 at Wembley Stadium in London.

“We all know what happened last time I was in a unification heavyweight championship fight. It was grueling. It was interesting, and we both left the ring with masses of respect,” Joshua said in a prepared statement.

“These fights aren’t easy because there is a lot on the line, so respect to Team Parker for taking the challenge. You know me. I love this game. I am looking forward to it.”

Parker, a powerful puncher with a rigid chin, said he is eager to land a heavy shot on Joshua, who was dropped by Klitschko in the April bout that many consider the favorite to earn 2017 fight of the year.

“Anthony Joshua is in for a huge shock,” Parker said. “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 A.J. can really take a punch. My entire existence is now devoted to proving what the boxing world already knows.”

Showtime is expected to televise the bout in the U.S., in what for now stands as the final fight on the premium cable network’s deal with Joshua.

That relationship is a compelling dynamic considering HBO, which has a tightening bond with Joshua promoter Eddie Hearn, is interested in landing Joshua.

Showtime is linked to unbeaten World Boxing Council heavyweight champion Deontay Wilder, who will defend his belt March 3 at Brooklyn’s Barclays Center against Cuba’s Luis Ortiz.

Should Joshua and Wilder win, that highly anticipated showdown would leave the winner standing as the first unified heavyweight champion since Lewis in 1999.