Complex sentence: He had begun a relationship with soprano Claudine Verneuil while still married to his first wife, but during his tenure in Seattle presented Claudine as his wife even though he had not divorced Troussier.
Split into simpler sentences: He had begun a relationship with the soprano Claudine Verneuil while still married to his first wife. However, during his tenure in Seattle, Claudine Verneuil was presented as Rosenthal's wife, even though he had not divorced Troussier.