Andrew Silverman feels "deeply betrayed" by Simon Cowell.
The New York businessman is still in shock at the discovery his wife Lauren Silverman is expecting a child with the 53-year-old media mogul and can't believe he let their flirtation go on right under his nose.
A friend told The Sun newspaper: "Andrew and Lauren had a great time with Simon. They were friends for over six years and often vacationed together.
"Andrew knew she was flirtatious - it's in her nature. To Andrew it wasn't a big deal. But there's a big difference between friends flirting and friends being sexual."
Andrew filed for divorce last month, naming the X Factor boss as co-respondent in the papers and citing adultery as the reason for the failure of their marriage.