The 36-year-old socialite - who is now estranged from her businessman husband Andrew - is expecting a child with the media mogul and hid her affair by telling her spouse she was seeing her parent.
According to reports in the New York Post, Lauren pretended she was going from her home in New York City to Miami, Florida, to visit Carole Saland.
The couple - who were friends with the 'X Factor' boss for more than six years - also have a seven-year-old son Adam.
Andrew filed for divorce last month, naming Simon, 53, as co-respondent in the papers and citing adultery as the reason for the failure of his marriage.
Simon is trying to get his name removed from the papers and is said to remain ''hopeful'' he will not be made to face court.
Carole has also spoken out to defend her daughter from critics, claiming her relationship with Andrew was not ''made in heaven''.
She previously said: ''Lauren isn't a gold-digger. She's a nice girl from Miami Beach.
''Her marriage was not a marriage made in heaven and life goes on, people go on.''
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The singer has donated half a million to relief efforts.
Pratchett died aged 66 in March 2015.