Lindsay Lohan discovered her father was cheating on her mum when she allegedly found him cavorting in a pool with the woman who was to fall pregnant with his lovechild.

In a new interview, conducted by Tv newsman Piers Morgan weeks before the actress checked into rehab in California on Friday (03May13), Lohan reveals she took a trip to her grandmother's home and found her dad Michael there with his mistress.

She says, "He'd disappeared for five days, so I asked mum if we could go to my grandmother's house and see if he was there. I got out of the car when we arrived and I saw him diving into the pool with some woman. So I ran into the house and checked her ID to see who she was.

"I remember running back to the car, feeling sick. I didn't tell mum until we got home. That woman was the one he had a secret child with, which came out in the press recently."

Michael Lohan accepted he had fathered a child with Kristi Horn Kaufmann earlier this year (13) after the Dna results were revealed during a Tv talk show. Horn and Lohan have reportedly come to a private out-of-court settlement regarding the outstanding child support. His daughter Ashley is now 17.