The actress who plays Suriyothai is actually a princess of a lower rank. In Thailand, each successive generation of royalties "decreases" in rank by one level. The actress is the lowest one. She is a "Mom Luang". One doesn't have to use the royal vocabulary with her.
Historically, all that is known about Suriyothai is her heroic death to protect her husband from the Burmese. The rest of the story in the film was made up.
The director is a prince, a "Mom Chao," which is two ranks below the conventional prince, the son of a king. People have to use the royal vocabulary with him.
In Thai history, the city Ayutthaya was burnt twice by the Burmese. This movie depicts the events shortly before the first burning. The second time the city was burnt was about 200 years later.
The wooden house on stilts where the young Suriyothai lives is a real palace called Tub Kwan. It is located in Nakhon Pathom, roughly 40 kilometers outside of Bangkok. King Rama VI built it.
The little boy-king in the movie is killed by hitting. This is because of a belief in ancient Thailand that the blood of a king or any royalties must never hit the earth. Therefore, they must be beaten to death by a club.
The actress who plays Chitravadee (the queen who died giving birth to Chai Racha's son) is in real life the wife of the actor who plays Khun Piren, Suriyothai's first lover, as an adult.
For release in English-language markets, extra footage was to have been filmed of Harvey Keitel as a foreign observer, but this plan was dropped in favor of re-editing.