I know a Secret Should I tell me Ex?

I haven't spoken to my X in 4 months. I know something she doesn't. I've known it for some time. I've been a friend of my X's Granddaughter for some time on My Space. My X at one time asked me to find out info on her Granddaughter so I joined her Myspace page. I really never talked to her Granddaughter but she list info on her page. Anyhow, her Granddaughter had a baby last week and says what she had and how much it weighs, even a name and she's posted pics of her and the baby in the hospital. My X's son is hiding all this from his Mom. However, his Mom knows from a friend who works at a nearby bar. The friend didn't tell details though so she doesn't even know the of the baby. Should I email her and tell her? Just to rub it in that I know and she don't? Will she find this strange that I know? What should I do?