Watson an haife shi ne a Paris, Faransa, 'yar lauyoyin Ingila Jacqueline Luesby da Chris Watson. Watson ta zauna a Maisons-Laffitte kusa da Paris har zuwa shekara biyar. Iyayenta sun rabu lokacin da take matashi; bayan da suka saki, Watson ta koma Ingila don zama tare da mahaifiyarta a Oxfordshire yayin da suke ciyar da karshen mako a gidan mahaifinta a London. Watson ta bayyana cewa tana magana da Faransanci, kodayake "ba ta da kyau" kamar yadda ta saba. Bayan ta koma Oxford tare da mahaifiyarta da ɗan'uwanta, ta halarci Makarantar Dragon a Oxford, ta kasance a can har zuwa shekara ta 2003.
Birnin Paris