After the sacking of Ayutthaya by the Burmese army in 1767, the royal palace was left abandoned and unused while the new capital of Bangkok was being established.
Not until the reign of King Mongkut (King Rama IV), was the Summer Palace re-occupied and renovated. This work was continued by his son, the Great King Chulalongkorn (King Rama V), and it is his version of the Royal Palace that you can see today. - Source
Not long after I had settled down in Bangkok, Kade's brother took me on a interesting river cruise from Bangkok to Ayutthaya, a former Thai capital. Before reaching Ayutthaya, we stopped off at the Bang Pa-in.