Wow, I almost just made a huge mistake (re: 3 Musketeers)

I had purchased a box set of The Three Musketeers which led me to believe it was a trilogy which included The Three Musketeers, Twenty Years After, and The Man in the Iron Mask. I was just about to start The Man in the Iron Mask when I happened to read the introduction, which mentioned the work "The Vicomte De Bragelonne". Boy, was I mistaken! I now know that the third novel actually includes The Vicomte de Bragelonne, Louise de la Vallière, and The Man in the Iron Mask. I almost just skipped way ahead without knowing it. Crazy! I guess I'm posting this so others don't make my mistake. Those who knew this already, feel free to laugh at my blunder. lol.

So this is the "3rd novel" lol I guess I have to read them all! Has anyone else read them?