Complex sentence: It has been said that she wanted to marry her cousin, Louis, the Dauphin of France, but this is probably not true; the surviving letters of her stepmother, Liselotte, prove that Marie Louise and the Dauphin were never in love.
Split into simpler sentences: It has been said that she wanted to marry her cousin, Louis, the Dauphin of France, but this is false. The surviving letters of her stepmother, Liselotte, prove that Marie Louise and the Dauphin were never in love.