The auction matters, as usual. The following defence, which makes use of the Obvious Shift Principle, is only poosible if North's primary suit is known to be clubs.
Here the
♦8 is encouraging wrt the Obvious Shift suit, clubs (Overcaller's suit). That doesn't necessarily mean, regardless of context, that South has a club honour (or club shortness), only that South prefers a shift to a low club* over a diamond continuation.
But here North knows that South knows that North can see that South would have discouraged the Obvious Shift (by encouraging a diamond continuation) without a club honour or club shortness. North also knows that South knows that North knows that if South has
♣Kx, then it's not only sufficient, but may also be necessary, to underlead the
♣A. So when North lays down the
♣A, South knows that it must be to cater for the possibility that South has club shortness. But South knows that North knows that that play can't gain a trick unless North also has the
♣Q. So South unblocks the K to make sure North is on lead after two club tricks.
* Instead of just a club shift. Encouraging the same kind of club shift (a low club or the A) both with
♣Kx(x...) and a small singleton club doesn't work in general, so I (currently) believe that if South wants North to play the
♣A and another club, he should play the
♦T (an unusually high diamond, intended as a wake-up signal) instead of the
♦8. The wake-up signal is also used on the relaitively rare occasions (compared with when he either wants partner to continue the suit or make the Obvious Shift) when the opening leader's partner is desperate for a shift to the remaining (non-led, non-OS, non-trump) suit, but hopefully partner if he really is awake, will see what's going on.
++++++++++++++++++++++++++++++++++++++++++++++++++
Rixi Markus recommended an A lead after an RHO pre-empt.
At double dummy, an A lead often succeeds, because you retain the lead, allowing an inspired switch.
Thus, here, GIB tells us the only fatal leads are ♠x or ♦x.
For example, after his ♦A lead, North can recover by switching to ♣s. If North switches to ♣A, South must unblock ♣K to get his over-ruff