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RA yesterday terminated the Wallabies and NSW Waratahs superstar's four-year, $A4 million ($NZ4.2 million) contract after an independent three-person panel found his controversial social media posts warranted his sacking.
Folau (30) last month posted a biblical quote which said "drunks, homosexuals, adulterers, liars, fornicators, thieves, atheists and idolaters" would go to hell unless they repented.
Castle said the decision would change the landscape for sport across Australia and perhaps internationally.
Folau later released a statement saying he was "deeply saddened" by the decision and that he was considering his options. He has until Monday afternoon to appeal.
If he decides to do that it will necessitate a second code of conduct hearing, which would add to the significant financial costs already incurred by both sides.
Folau has reacted to the sacking with another post on Instagram.
Castle said there had been discussions between both sets of lawyers regarding a possible payout to Folau, but they had never advanced far enough to be brought to the RA Board.
Asked if RA could have better handled the situation regarding the negotiations of Folau's last contract Castle said: "You couldn't go through an issue like this and not say that you couldn't do things better.
"You'd be crazy to say that. But it's often done with the benefit of hindsight and the sequence of events that happen.
"So out of this we will certainly do that review to make sure we understand that we' have got the right contracts in place.
"That will be a discussion that we will need to have with RUPA (Rugby Union Players' Association) around whether the code of conduct is delivering the best outcomes from a financial delivery viewpoint.
"That will be something that we'll be looking to discuss with them as we come to a new collective bargaining agreement."
Castle explained RA couldn't insert a specific social media clause in Folau's last contract as it wasn't part of the existing CBA between RA and RUPA.
'"We can't just insert clauses whenever we feel like it," she said.
'Even if we had a (social media) clause who knows where this could have gone from a legal perspective?'
Asked if the CBA could be updated in future to keep pace with the development of social media Castle replied: "I certainly think those are the types of things that CBAs need to include and as time changes and social media does become more focused."