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The victory took the 35-year-old's professional record to 20 fights undefeated while Joshua, 32, suffered a third defeat in what could prove a watershed in his career.
Foreman said the two women have been trying for the past six months to get "millions of dollars" each from him and his family.
Tyson Fury emerged unscathed from a turbulent fight week to cement his place among the greats of heavyweight boxing with a stunning TKO win over Dillian Whyte.
Fury will likely now look to take on Ukraine's Oleksandr Usyk, who holds the other three titles, for a chance to become the first undisputed heavyweight champion since Lennox Lewis 21 years ago.
Usyk seized the WBA, WBO, IBF and IBO belts with the three judges scoring it 117-112, 116-112, 115-113.
The 'Clash on the Dunes' in Diriyah was for the IBF, WBA, WBO and IBO titles and Joshua set the pace from the start with a measured masterclass that showed he had learned from the nightmare of New York.
American Wilder won after a split decision draw with Britain's Tyson Fury at Staples Center in Los Angeles, leaving both fighters talking up a rematch.