Simplify the following text for a Grade 11 native English-speaking person.
Original: The Palace of Holyroodhouse , or informally Holyrood Palace , founded as a monastery by David I of Scotland in 1128 , has served as the principal residence of the Kings and Queens of Scotland since the fifteenth century .
Simplified: Holyrood Abbey was founded by David I , King of Scots in 1128 , and Holyrood Palace has served as the principal residence of the Kings and Queens of Scots since the 15th century .