My real father....need some advice

So I finally found my real dad that signed his rights over when I was 3 I'm now 28 and found him. I've never met him just talk on the phone. But my mother is now remarried and doesn't know I have found him and speak to him. She doesn't talk about him to me or anyone not even sure she's told anyone that I have a different father then my sister's. I hate keeping this from her but I don't want to ruin our relationship if I tell her I talk to him and eventually want to see him. I just need some outside advice. My husband says to tell her but I'm just not sure how to even go about that conversation with her. Thank you in advance. ♡