Sonny Bill Williams reportedly lent more than half a million New Zealand dollars to close friend, Australian boxer Anthony Mundine.

The Sunday Telegraph in Sydney reports that Williams loaned NZ$532,000 (R5,093,346) in a handshake deal in order to help Mundine deal with a personal issue.

Apparently, Mundine previously lent Williams NZ$800,000 (R7,659,167) in 2008, and that Williams was happy to return the favour.

'It's very hard to explain our brotherhood in words,' Mundine said. 'I didn't understand it until I became a Muslim. We trust and we love each other.

​'We'd literally die for each other. It's all about being there for each other … I'll pay him back as soon as I get paid next week.'

Williams, who will play for the Blues in Super Rugby this season, is still recovering from an Achilles injury sustained last year.