Thanks, I do appreciate all comments above. This was a real hand happend at my bridge club's team league two monthes ago. I assume that it is rare to hold such a hand at South's seat in such an auction so that the response would be a real challenge even for regular partnership at expert level. At the open table, the south(our opponent) bided 4♠ to show a strong hand and probably implied other 2 suits, but the north believed it was strong raise to ♦ suit and they finally reached 7♦ which was 3 down as ♦ break was 5-1. Trust me, North/South were expert players and regualr partners. I am wondering that is there anyone playing 4NT as a sort of convention which could show such a hand here? As 4♠ cuebid is always available to show a strong hand with ♦ support, why do we need to keep 4NT as ♦ RKC Blackwood here?