Complex sentence: His first dancing partner was Jimmy Stewart's wife, Gloria Hatrick McLean, however, he was informed that she was too tall for him and Murray advised him to begin working with a young blonde débutante named Vivian.
Split into simpler sentences: His first dancing partner was Jimmy Stewart's wife, Gloria Hatrick McLean. However, he was informed that she was too tall for him, and Arthur Murray advised him to begin working with a young blonde débutante named Vivian.