Introducing an intact puppy to a neutered adult - any advice?

Hi,

I have a seven year old bulldog who is neutered. We have been asked to take in a 6 month old boy due to a relationship breakdown. Obviously the pup hasn’t been done yet.

We introduced them outside today outside in an open area, things were going okay then my dog started to growl and act aggressively towards the pup. We separated them and carried on walking with me being ahead of my husband who had the puppy. Occasionally we tried to introduce them again but before long the same thing would happen.
After about 3/4 attempts we stopped as we didn’t want to make the puppy scared and my dog was panting excessively which he does when he’s worked up.

I really want to make this work but I’m not sure how to do it. My dog hasn’t been aggressive to other dogs before, in fact he’s usually submissive when he gets started on, but we don’t have experience of him being around an intact male before so this is new to me. He mainly socialises with female dogs.

Can anyone offer any tips or advice? I would really appreciate it!

Thanks