Bidding on when you realise you have made the wrong bid
North has 6/6 in the minors and 16 points. He opens 2D announced by his partner as weak. There is an overcall of 2 spades and his partner with 4 points and 4 diamonds competes with 3 diamonds.
North then bids 6 diamonds which makes.
Only 4 players in a field of 15 tables has bid the slam. North says he forgot they were playing weak twos and thought they were playing Benjy 2 diamonds which is game forcing.
He denies having heard his partner say weak, but the opponents both heard it.
I am called at the end of the hand rather than at the end of the auction.
What action should I take? Can I allow them to play in 3 diamonds + 3?
When I suggested this North got quite annoyed and said it was obvious that he had made the wrong bid, and anyone would have done what he had done?