Question about breastfeeding Irish twins.

Annie

My son is 3 months old and I just found out that he is going to have a little brother/sister in a couple of months. For various reasons, I stopped breastfeeding him 2 months ago but I hope to be able to breastfeed my future baby for a lot lot longer. Now I was wondering, will it be safe for him to "resume" breastfeeding after a year with the milk produced for the newborn?