Question abut when a main gauche attack occurs in the round

[raniE]

So, I got my legacy edition box on Wednesday and played my first game of melee in around fifteen years today. Ran into a question almost immediately. When a fighter attacks with a regular weapon and a main gauche, does the main gauche attack happen simultaneously to the main attack, at the adjusted DX rank (so 4 DX slower than the regular attack), or last in the round (like with bows firing multiple shots)?