Here's what you need to know:
Aged 28 the big Brit has won all 20 of his fights by TKO. South Auckland born Parker, aged 26, has won all 24 of his fights, 18 coming by TKO.
Joshua currently holds the WBA, IBF and the IBO titles however the IBO sanctioning body is not regarded as one of the leading bodies known as the 'big four'.*
He won the IBF title after a knock-out win over Charles Martin in 2016.
He then added the WBA and IBO belts when he defeated long reigning champion and legend Wladimir Klitscho last year.
Parker defeated Andy Ruiz in 2016 for the vacant WBO title left by Tyson Fury after a drug scandal led to him having to step away from boxing.
There is also the WBC belt held by American Deontay Wilder the last body of the 'big four'.
The winner between Joshua and Parker will in theory go on to face Wilder in hopes of ultimately unifying all four of the heavyweight division belts, becoming the undisputed heavyweight champion of the world.
No one has ever unified all four.
Joshua is also a Super Heavyweight Olympic Gold Medalist and is ranked as the world's best active heavyweight.
The fight between the two champions will take place at the Principality Stadium in Cardiff in front of a sell-out crowd of over 80,000.
This fight is being shown live on Sky Arena with the under card starting at 5am with the main event expected to start before 8.30am.
*In boxing there are four leading sanctioning bodies each with a separate title a boxer can hold. These are the WBA (World Boxing Association), WBC (World Boxing Council), IBF (International Boxing Federation) and WBO (World Boxing Organisation). In 1963, two commissions evolved into the WBA and WBC forming the two original "sanctioning bodies". Then in 1983 the IBF and WBO were formed separately again.
