Wallabies back Nathan Grey's deep, dark secret has finally been revealed.

Grey's mother is a Kiwi.

The inside centre was thrust into the spotlight when named on the Australian bench for Saturday's Rugby World Cup semi-final in Sydney.

He was asked by a New Zealand journalist about his Kiwi roots and reluctantly admitted his mother's heritage.

But it wasn't a topic on which he wanted to dwell.

Is it a dark family secret, asked another journalist? "It is for me," Grey said.

The NSW Waratah was happy to talk about his inclusion for the long-awaited trans-Tasman encounter, touted as a "Bledisloe on steroids" by one scribe.

The 28-year-old has been champing at the bit after being given a taste of World Cup rugby against Namibia.

His last Test before that was playing five-eighth against England in June, where he filled in ably for the preferred No.10, the injured Stephen Larkham, and the dumped Elton Flatley.

He then frustratingly found himself on the outer for the Tri-Nations series.

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