After a bidding where opps keep silence you arrive in 7NT played by South with a ♠10 lead. You see:

Counting top tricks you get to only 8: one spade + two hearts + two diamonds + three clubs. Not very encouraging... Obviously you must play on diamonds and guess the ♦Q to have a chance for 13 tricks. The lead looks like the top-of-nothing, it's 99.9999% that West doesn't have the ♠K... So you put the ♠A, get in hand with a high club and cross your fingers for a diamond finesse to the Jack. It holds ! Ok, but you are not done... ♦K, ♣A and another club to get back to hand and you start running the diamonds. Clubs and diamonds split, good news! You know East has the ♠K and you hope that also he has the ♥Q so he will be squeezed when you run the diamonds. Playing to finesse twice for the Queen in West hand in a grand slam is really to much...The situation of the last four cards is this: 

When you play the ♦A East will be squeezed in spades and hearts. He can't throw the ♠K or your Jack will be high and if he is discarding a heart you will simply cash the last three hearts tricks in force. Bridge luck was with you and you make all 13 tricks. Well done declarer ! Only side comment is: Next time you bid a grand try to have an easier way to 13 tricks and at least 75% chances to make. Otherwise you might get into the stupid situation when you go down in a grand and at the other table the opps are only in game... The full hand was:

Seeing only NS hands probably a 6♦ contract is the percentage bid, but for sure 7NT gets a lot more adrenaline in your blood as declarer!