I've been told it changes a few details, but how much? Did William Wallace actually sleep with the French princess or whatever? Was longshanks son a homosexual? Sorry if this as already been asked before
It's pretty famously inaccurate honestly, I would take anything it shows with a couple dozen pounds of salt.
A couple quick points -Will Wallace was almost certainly born into the aristocracy, not some salt-of-the-earth farmer -The "Right of Prima Noctis" is pretty much complete bullshit, and certainly wasn't something the king of England used to lord over Scotland. -Isabelle of France was something like four years old during the events of the movie, and never met William Wallace regardless. So they almost certainly never slept together
There's a lot more inaccuracies in the film (Kilts weren't popular for another couple centuries, for one) but those come to mind. It's a fun movie, but REALLY not historically accurate.
This question does get asked every now and then, like in this thread
The point made below about Isabelle of France being three or four at the time is indicative of the historical accuracy of the film. So even if William Wallace had slept with her, it would not have been quite as romantic as depicted in the film.