Dermot Desmond is to underwrite a $95 million Canadian dollars (€66 million) fundraising by Mountain Province Diamonds, of which he owns a stake of about 25 per cent.

Des Sharkey, the veteran Irish property developer, is also a shareholder in MPD.

MPD, which owns 49 per cent of Gahcho Kue, a huge new diamond mine in the Canadian tundra, told the Toronto stock exchange the money was to fund a “cost overrun” fund that was a condition of another $370 million debt facility.

Mr Desmond, who also backs MPD spin-off Kennady Diamonds, has committed to “fully exercise his rights” under the rights issue and will also take up the rights of any shareholders who choose not to take part.

He will receive a fee of 3 per cent of the funds raised for underwriting it.

The Gahcho Kue mine, which is due to enter production in 2016 and will be operated by its majority owner De Beers, is sitting on diamonds worth $20 billion.