That's because they're very closely related languages. English is a mix of Anglo-Saxon and Norman French, after the Norman invasion of England in the 11th century. Norman French is how the Norse diaspora in Normandy mixed their Germanic tongue with the local dialects of Latin. And the Romance and Germanic languages are both pretty closely related branches of Indo-European, which is also a pretty narrow language family to start with. For example, 'tu' from French comes from mixing Norse 'du' with Latin 'tuus'...both of which come from deeper roots. Proto Indo-European reconstructs this as 'tuH'.