Blessing in Disguise by Danielle Steel

As a young intern at an art gallery in Paris, Isabelle McAvoy meets Putnam Armstrong, wealthy, gentle, older and secluded from the world. Her time at his Normandy chateau is the stuff of dreams, but when she learns she is pregnant, she knows that marriage is out of the question. Returning to New York, Isabelle enters a new relationship that she hopes will be more stable but before long she realises she has made a terrible mistake and once again finds herself a single mother. With two young daughters Isabelle unexpectedly finds happiness and a love that gives her a third child, a baby as happy as her beloved father. And yet, life brings more change.