She sent sexy selfies to her lover shortly after his wife died.
The shocking admission came when Gypsy Willis, the ex-mistress of the doctor on trial for killing his wife, took the stand again.
The prosecution asked Willis, "What are these pictures showing?"
"Me lying down on a pillow," she replied.
The prosecution then asked, "Will you describe the content of these two pictures."
Willis answered, "They are of me in a mirror exposing my back."
Dr. Martin MacNeill is accused of drowning his wife Michelle in the bathtub as she recovered from a facelift, which she got at his insistence.
Prosecutors said he killed her so that he could be with Gypsy Willis, a nursing student. MacNeill has pleaded not guilty.
After his wife died, MacNeill hired Willis as a nanny for his younger children and moved her into the family home near Salt Lake City.
The prosecutor asked, "And the two of you resumed your sexual relationship and the two of you were hiding the fact that you were sexually involved from the children?"
Willis replied, "Yes."
Nancy Grace is covering the trial for HLN, and she told INSIDE EDITON, "The gall it took for Dr. Martin MacNeill to move her into the home as the move-in nanny when she was really his lover."
Three months after Michelle died, Willis said she and the doctor began looking for wedding rings on the website Bidz.com.
"What kid of a ring was this?" asked the prosecutor.
"It was a diamond ring," answered Willis.
When questioned on the ring's size and cost, respectively, Willis answered, "4.5 karats and around $7,000."
The wedding never happened, but Willis took MacNeill's name anyway.
During cross examination, MacNeill's lawyer, Susanne Gustin, went after claims that Willis did not perform actual nanny duties.
"What were your nanny duties?" asked Gustin.
"I would get up and make sure they were getting ready for school and getting breakfast, Then, I would take them to school." replied Willis.
INSIDE EDITION's Paul Boyd asked Nancy Grace, "Is the prosecution doing a good job proving the case beyond a reasonable doubt?"
Grace replied, "Right now, the State has laid out an excellent case on motive but as soon as we get into forensics, such as cause of death, it is going to be very deep waters for the State."