Telling the news

My son wants to tell his grandma I’m pregnant so bad, I was with my sons father for 5 years a bad relationship, I got out of it & was single for 2 years finally I met my a nice guy and after a while we got married. Now I am pregnant ahaha obviously but my son wants to tell his grandma I’m pregnant, I am close to my ex mom she is nice lady & helps me since sons father isn’t around. I just don’t know how I feel about telling her. Anyone gone through this? How long did u wait to tell ur ex family ? & how did it go?? Thanks in advance.