Looks really weird man, could be what ZZ said but, with heat stress you usually get the pistils growing out like crazy. You don't seem to have any pistils. Broad mites kill off pistils, but it doesn't really look like broad mite damage... Sorry you got me!
Edit: ok wait if you only got it on one part of the plant then I am thinking broad mites!
How many days has it been in flower?... Maybe go check out the broad mite thread above, to make sure it is not that. It's been a long time since I had late flower buds affected by broad mites so I am not sure. Pistils turn brown from broad mites, maybe you noticed that earlier in flower?