Complex sentence: For the sixth and seventh seasons of "The Voice", Aguilera was respectively replaced by Shakira and Gwen Stefani, but she will be a coach again for the eighth season.
Split into simpler sentences: For the sixth and seventh seasons of "The Voice", Aguilera was respectively replaced by Shakira and Gwen Stefani. However, it was announced that she would serve as a coach again for the eighth season.