You are sitting East holding ªQ10xx. xxx. J. §Axxxx

Clearly the opposition have the Ace of Diamonds unless they're prone
 to calling a slam missing two aces and north either has it or a
 second round control after his jump to 4nt.For a diamond lead 
to be right partner has to have a secondary diamond winner plus 
an entry in which case there liable to go down whatever you lead.

Could it be a spade if partner has the king? Could the two hands be

North:ªAxxx AQJxx x §KQx

South: ªxx K10xx AK §J10xx
It dosen't matter what you lead
If declarer had a 6th heart and one less spade a spade lead is right
but why should partner have the king of spades
Ok Poirot I think you've got it

Put your ace of clubs on the table, there's no case for leading a 
diamond and a spade is remote and your partner will be very happy 
when he ruffs the second club. It was missed on okbridge and pard
did have a trump but it's easy when you're spectating.