The Norman invasion massively affected the Anglo-Saxon language. It affected most of his inflections and some german words, incorporating new words. The Norman conquest changed the course of the english and the conquest of one people by another brought changes in the way of speaking. As a new nobility was introduced, little by little, the influence in communication was affected.
Here are some examples of embedded words that have undergone some flexing or modification due the french domain (original english words in the left side - incorporation/ modification of french word in the right side)
Swine / Pig - Pork/ Porc (french)
Kingly - Royal (french)
Buy - Purchase (french)
Dove - Pigeon/pijon (french)
betrothal (out of use) - Proposal (french)
tough - Difficult (dificile, dificulté) French