Complex sentence: Romana remains one of only two members of the Doctor's own race to travel with him during the entire television series, the other being Susan Foreman, the Doctor's granddaughter, although Susan was never explicitly designated as a Time Lord.
Split into simpler sentences: Romana remains one of only two members of the Doctor's own race to travel with him during the entire television series. The other member of his race to travel with him was Susan Foreman, the Doctor's granddaughter, although Susan was never explicitly designated as a Time Lord.