Casey Anthony father’s stunning confession to his secret mistress in an exclusive criminal investigation interview.

While searchers desperately hunted for missing Caylee Anthony, the 2-year-old’s granddad George was busy carrying on a torrid affair with a secret mistress, The ENQUIRER has learned exclusively.

Now his mistress Krystal Holloway has broken her silence in a world-exclusive ENQUIRER interview – revealing that a tearful George confessed how the adorable little girl died at the hands of his daughter Casey.

Until Caylee’s skeletal remains were found in December 2008, George insisted publicly that he believed his beloved granddaughter was still alive.

But during pillow talk, his mistress says he revealed why he was standing behind Casey, saying: "My daughter has done a lot of things, but this is it! I know what she’s done to my granddaughter – but I can’t bury another child."

Krystal was interviewed recently by police, The ENQUIRER has learned, and is a potential witness in the case. She says she has told investigators about George’s private revelations about little Caylee’s brutal death.

The 38-year-old mistress, who lives near the Anthony family, told The ENQUIRER: "George was in tears when he told me what happened.

"I had told him, ‘I don’t think I could fall in love with somebody who could raise a daughter who would kill her child.’

"George gripped my hands and turned to me with tears filling his eyes. ‘It was an accident that snowballed out of control,’ he said.

"’You know, when you tell a lie and think it’s a small one?…then it just keeps getting bigger and bigger?’

"I didn’t know what to say to comfort him. I realized he’d just told me he knew how Caylee died – and that Casey was responsible."

The full interview is in the latest ENQUIRER – still on sale.