By Breaking Celebrity News Staff

In a bizarre moment, Lindsay Lohan acted surprised when asked on Friday’s Good Morning America about this week’s widely-reported news that she had a secret half-sister.

When GMA’s Amy Robach broached the topic that her dad Michael had recently been given positive DNA proof that he had fathered a child, now 17-years-old, out of wedlock with a former mistress, LiLo replied: "I didn't even hear that, so thanks for the news!" (She didn’t hear the news?)

Lindsay was on GMA to promote her upcoming Lifetime movie, Liz & [expletive], and most of Robach’s questions were generic, if not softball. Robach’s follow-up to LiLo (stunningly) laughing off news of her having a secret half-sister: “How does your family handle all those headlines splashed daily?”

Robach -- who proclaimed the movie “fantastic” at the top of the interview -- didn’t exactly channel her "inner Barbara Walters" and ask specific, hard-hitting questions of the Mean Girls star, 26, who’s had more than her share of legal trouble and family drama.