There is disclosed an air-oil separator for a gas turbine engine. The separator has a first separator section having a first separator rotatably mounted about a rotation axis and having an air-oil mixture inlet and an air-oil mixture outlet; a second separator section having a second separator rotatable about the rotation axis, the second separator having a first air-oil mixture inlet fluidly connected to the air-oil mixture outlet of the first separator, and a second air-oil mixture inlet; and an air outlet. A first flow path extends from the first air-oil mixture inlet to the air outlet through the two separator sections, and a second flow path extends from the second air-oil mixture inlet to the air outlet, solely through the second separator section A method of operating an air-oil separator is also disclosed.