It is extremely rude for children to interupt other people who are speaking. It is also rude to hog the conversation and not wait for the other person to have a turn.
Children are not allowed to behave like that in school.
You need to take charge and act like the parent. Instead of being miffed and upset for your self, be upset for DS that he is not being taught common good manners.
Start saying - Stop, DS, did you hear that another person is talking? It is very disrespectful of you to interupt another person while they are talking. Please use your ears.
Then the next day - Stop. Wait DS. You can hear that Daddy is still speaking. Please wait.
Wait DS, it's Daddy's turn to speak. You have had your turn.
After a week say - Wait DS, please use your good manners.
After a good while - Wait DS, if you have to be reminded to use respect and listen when some one else is speaking then you have no manners at all.
If DS still interupts after a month of you knowing he understands the rules of polite conversation, send him straight to his room until he is ready to use his own ears better and take turns at speaking.
It is very immportant that you and your DH also need to model the same respectful behaviour of not interupting another person when they are speaking.