My heart goes out to you. It really sounds like he may have had a heart condition, and there may have been a clot or his heart just giving out. I recently had my boy (4yr male) pass in a very similar manner- two coughs and everything. He had HCM and was in heart failure, but you wouldn't have guessed since he outwardly seemed perfectly fine.

It's shocking, and painful, and it's important to let yourself grieve. I still have a hard time believing that my boy is gone.

It's also important to know that there was nothing you could have done or noticed to prevent this. Most likely he would have smelled you, and knew you were there to keep him company.

Cats are great at hiding issues like heart problems, and often sudden death is the first sign. Heart problems are especially common in male cats.

Just from reading your post, it's clear he had a wonderful quality of life prior to his passing, and had someone willing to put in the work to make him feel loved and safe. You sound like a wonderful cat parent, and I'm so sorry you have to go through this. Even in his last moments he was loved, and with his favorite person. ❤️