Don't ask Lindsay Lohan about the 17-year-old half-sister that her dad Michael Lohan reportedly fathered out of wedlock. Because she won't even know what you're talking about.

"I didn't even hear that, so thanks for the news," Lindsay said earlier today (Nov. 16) on Good Morning America. "I don't pay attention to any of it. I can't. I don't really want to get into that because I want to stay on the positive side of things."

On Thursday's episode of The Trisha Goddard Show, a DNA test revealed that Ashley Horn is the daughter of Michael Lohan. Her mother, Kristi Horn, said that she had a fling with Michael back in 1995. At the time, he was separated, but still married to Dina Lohan.

Kristi informed Michael about Ashley in 2005, following a paternity test that didn't match with her ex-husband. Michael took a DNA test in 2008 and has been listed as the father on Ashley's birth certificate since December of that year, after he failed to show up in court in Montana for a paternity hearing.

Up until yesterday he'd denied he was Ashley's father and refused to pay child support.

[via E! News]