The practicing Muslim has two daughters and a son with wife Alana Raffie, who he married in 2013.
The couple's first daughter Imaan was born in 2014, his second daughter, Aisha, was born in December 2016 followed by son Zaid last June.
After attending an All Blacks training last week, Prime Minister Jacinda Ardern revealed the Williams asked her she was planning on expanding her family.
"I was just talking very briefly with Sonny Bill about preparation and he changed the conversation quite quickly. Look, he was trying to encourage us to expand our family. I was just encouraging him to win the game," Ardern told reporters in Japan today.
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