The former glamour model says the media mogul shouldn't have any ''regrets'' after he embarked on a relationship with the New York socialite - with who he now has two-month-old son Eric - while she was still married to his friend Andrew Silverman, with who she has son Adam, eight.
In her column for Now magazine, Katie, 35, wrote: '' People have affairs for all sorts of reasons - because they're bored, crave taking a risk or want to inject some spice into their life.
''Some can be short lived, some are secrets taken to the grave and others become the beginnings of a new relationship. These things can and do happen and they'll continue to happen.''
The comments come after Simon recently spoke out to say his affair with Lauren is not something he's ''proud of'', but Katie claims the birth of their son Eric was a positive outcome in the situation.
Katie - who has eight-month-old son Jett with husband, Kieran Hayler and three kids, Princess, six, Junior, eight, and Harvey, 11, from previous relationships - added: ''So don't have any regrets, Simon. Live life with your family and don't worry about what others think.''