My dog met little kitten

[u/chrisalvarado]

So on Sunday, my gf decided to finally introduce her new kitten to Mikie , my dog (1.8 years old male, mixed breed). She got her (Lulu, the kitten) last Wednesday and she was a bit scared and worried about having them meet. Short background on Mikie, he is a very sweet dog but very VERY hyper. Often jumps on people, plays 24/7, you see where I’m going. But he’s also a very shy and timid dog. When he sees people or dogs, he pulls and runs to them but then stays still and like runs always sometimes to later come back. With dogs he lets them sometimes hump him which is concerning but not the issue here lol. Well the frost reaction when Lulu came over and was held by my gf, Mikie just sniffed and sniffed and lulu hissed at him, expected but then he got too close and she hissed very loud and took out the claws. Then he went again to sniff but later she did it again loud and he got a little too scared or excited or idk that he wanted to like jump kinda on her which my gf said wow that was scary and I told her no no you know he never bites or anything. Well he kept sniffing after she sat down and I kept an i on him, he was very excited and all panting and all and after a while before she was going to leave. We did the same thing but this time Lulu was not looking so I said perfect time for Mikie to sniff again and so he did and she didn’t notice, he even started licking her ear but out of nowhere in a split second lulu saw him and hissed very loud again and I was holding Mikie by his collar and when he heard Lulu hissed like that he immediately opened his big mouth and went straight to her head. No growling or anything just immediately jumped to bite her head/neck , mainly head though and I had him by the collar and pulled away almost instantly and I pulled away so hard that even the collar broke off him and he fell to the ground. I got very scared and my girlfriend did too that she took lulu upstairs to my room and was shaking and crying because he went straight to the head. He does not have a history AT ALL of biting, he’s very sweet and good boy that gets in my nerve sometimes lol, but still NEVER aggressive and I got him when he was 8 weeks old. So I never ever let him be aggressive to anyone or anything so I was very shocked and disappointed at him and my gf was too….. does anyone have any idea as to why maybe he did this? Keep in mind that my gf had lulu on her blanket and on her arms all the time at my place. We NEVER expected for this to happen ever… we expected the hissing but not this much… she’s a baby, 8-9 weeks old. I have plans of proposing to her in the next couple of months and you know they will have to live together so how can we fix this… neuter animal is aggressive at all. Help please?