Brother & Sister by Joanna Trollope
Nathalie and David have been good and dutiful children to their parents, and now, grown-up, with their own families, they are still close to one another. Brother and sister.
Except that they aren't - brother and sister that is.They were both adopted, when their loving parents, found that they couldn't have children themselves. And up until now it's never mattered.
But suddenly, Nathalie discovers a deep need to trace her birth parents and is insisting that David makes the same journey. And through this, both learn one of the hardest lessons of all, that sometimes, the answers to who we are and where we come from can be more difficult than the questions ...