When is a good time to tell my boyfriend we are expecting.

When is a good time to tell my boyfriend we are expecting? He has a nine year old from a previous relationship. We were not intending on getting pregnant, so I am a little nervous about telling him. I haven't had my first appointment yet and was thinking of waiting till then. But it's so far away. I also don't want to tell him in front of his daughter as I want him to know first. Unfortunately we haven't had any alone time for me to tell him. So I guess I have a conundrum.