Is beating the "final" boss a requirement for act 3 ?

I did every wish on every board, beat groal, opened every ventrica station, found all 5 delicacies, finished Shakira's quest, awoken the sentinel, even beat that lady in the exhaust organ and still nothing. Some people didn't even mention beating lace to get act 3 but some do so I'm a bit confused, can anyone clear this up ?