Complex sentence: Phelekezela Mphoko, the Second (and only sitting) Vice-President at the time of Mugabe's resignation on 21 November 2017, he may have been acting President of Zimbabwe for three days until Mnangagwe's accession to the presidency.
Split into simpler sentences: Phelekezela Mphoko, was the Second (and only sitting) Vice-President at the time of Mugabe's resignation on 21 November 2017. Mphoko may have been acting President of Zimbabwe for three days until Mnangagwa's accession to the presidency.