[UconnTim97]

Keep them separated if possible and introduce them with short supervised visits. Let the visits get longer as they get more accustomed to each other. Keep them occupied during these visits.
We did this last year when we introduced a new kitten to our now 8 year old cat. It took almost four months mostly due to he kitten being so small compared to the older cat. They get along as fine as a kitten and an adult cat can now.
In our case, the kitten was approximately four weeks old when we found her. It shouldn't take you half as long.
Best of luck.