Declarer could not avoid the loss of a diamond trick and the grand slam was down one, N-S -100.
North's splinter bid promised a singleton club, an opening bid and four-card spade support. South cue bid the ace of diamonds and North reciprocated by showing the ace of hearts. Blackwood subsequently disclosed that North also held the king and queen of spades and one other king. South knew that partner held the king of hearts because he would not splinter with a singleton king.
North's distribution was known to be either 4,4,4,1 or 4,3,5.1. He would have responded two hearts when he owned a five-card suit. However, he might have elected to bypass an emaciated five-card diamond suit.
South's resolve to venture a grand slam was too risky. All would be well when North displayed the queen of diamonds but declarer would require help otherwise. If partner held four diamonds without the queen, South would need a doubleton queen or perhaps a finesse when North produced the jack and ten. South should, therefore, have settled for a small slam.