Complex sentence: On 12 September, she announced her fourth album "R.O.S.E." and the single "Think About That", which was released on 15 September 2017 as the album's lead single.
Split into simpler sentences: On 12 September, she announced her fourth album "R.O.S.E." and the single "Think About That". It was released on 15 September 2017 as the album's lead single.