It seems Lindsay Lohan got an unwelcome surprise over the weekend: an announcement of a new baby sister.Except the announcement wasn’t for a baby, but a 13 year old sibling none of the Lohan’s knew existed until last week.

More pics after the skip…

The Lohan dad - Michael - seems to have had an affair with a woman during his brief separation from mom Dina back in 1995.  The result - a love child who is now 13 years old!  Just what the Lohan’s needed to enjoy a calm summer for once…a sibling scandal!

Michael quickly piped up and said a paternity test proved she was his via TMZ.  No comment from Lindsay, or sister Ali or mom Dina for that matter.  But hold on, these women don’t keep quiet for long and somebody will have something good to say!  Who will speak first?

Photos: PR Photo