The Melbourne Rebels rugby player, who dated Brook between autumn 2008 and summer 2010, revealed that he found out she was expecting her first child earlier this year.
He told The Mirror: "Kelly told me in January that she was expecting. I'm really happy for her. She will be a great mum."
The model and actress revealed on Twitter yesterday that she and partner Thom Evans are expecting a daughter.
She has since taken to the social networking site again to thank fans for their "lovely messages".
Cipriani and Evans played together for London Wasps between 2004 and 2006.