@ Not how, but why?
"what persuaded him to keep his mouth shut?"
Possibly because he thinks that such things are nobody else's business, certainly not that of the muck-raking gutter press.
Exactly what "public interest" is served by a prurient, lip-smacking "expose" of this women in a rag like the Mail on Sunday? Answer: None.
It's nothing but salacious tittle-tattle designed to let middle England tut at the collapse in morals of our society and the fact that splashing someone's private life over its pages might ruin their (entirely unrelated) career doesn't matter to them in their quest to peddle more of their trash.