Oh Fig, I am sorry. Please don't have your dog put down unless the agression continues.
This is a natural thing for dogs. You should never leave young kittens around dogs.
The dog has just had a move to contend with, maybe he has been abit neglected and then the cat had kittens, so lots of attention for cat and kittens-maybe a bit of jealousy there.
Understandable he isn't keen on BH right now depends how severe the punishment was.
If the aggression continues and is very out of character it could be the dog is ill- possibly a tumour.
My dog is over 100 pounds and a real gentle giant but he gets a little jealous when I have my g/son.
Re enforce your position as alpha male in the pack and lots of love and affection.
The dog will have forgotten kitten inciddent shortly after. Just a life lessson for Hardy. It's hardy but happens. Please don't let it affect his love for the dog or animals in general.Afterall the kitten would have grown up and killed and eaten lots of animals smaller than herself. Survival of the fittest.
Always remember however pampered, however good the pedigree a dog is a step away from a wolf.
That said I would never be without one, my life would be so much poorer without my best friend.