Did Princess Dianas mom have an affair?

Diana confirmed her affair with horse riding instructor James Hewitt. He had initially been summoned to instruct William and Harry, but as the relationship ensued, Diana herself gathered the courage to overcome her childhood fear of riding. The affair started in 1987 and lasted 5 years. It started cooling when Hewitt was dispatched to Germany in 1989 and served in the Gulf War in 1991.