Rory Stewart conceded that "nothing with Mugabe was inconceivable" after the Zimbabwean president refused to step down despite his Zanu-PF ruling party demanding his resignation.
The 93-year-old leader’s days have been numbered since last week’s military intervention, which came in response to Mugabe’s sacking of vice president Emmerson Mnangagwa.
It had been feared that Mugabe’s 52-year-old wife Grace would succeed her husband as leader but Mr Mnangagwa is now expected to take over in the coming days.
Mr Stewart described Mugabe’s 37-year rule as a “brutal tragedy” for Zimbabwe but Mr Mnangagwa’s desire to take power in a way that was "constitutional and legal" could give the opportunity to have fair elections.
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GETTYRory Stewart believes the ousting of Mugabe will offer Zimbabwe new opportunities
He admitted he remains “sceptical” about Mr Mnangagwa, who has been nicknamed ‘the Crocodile’ and has been part of Mugabe's government for much of his time in office.
However, he said the end of Mugabe’s rule represents “a moment for change”.
Mr Stewart said Mr Mnangagwa would also be "reaching out to Britain and others because he will want legitimacy" although the change must be led - and seen to be led - by Zimbabwe.
He said: ”Mugabe was a tragedy, a brutal tragedy,