Simplify the following text for a Grade 9 native English-speaking person.
Original: The Norman conquest of England began on 28 September 1066 with the invasion of England by William , Duke of Normandy , who became known as William the Conqueror after his victory at the Battle of Hastings on 14 October 1066 , defeating the then king Harold II of England .
Simplified: The Norman conquest of England was a military invasion of England by William the Conqueror in 1066 .