Diamonds really are a billionaire’s best friend.

Dermot Desmond has in recent weeks bought another one million shares for about €3.5 million in the Canadian-listed company Mountain Province Diamonds (MPD), boosting his stake up to a hefty 22.3 per cent.

Desmond previously took part in a Cnd$45.4 million private placement by MPD last month. He effectively off-loaded the new shares he acquired in that transaction, however, in a “private off-market transaction” for about €7 million to an unnamed investor.

The Daon founder, whose long-time associate Jonathan Comerford chairs MPD, is now firmly ensconced as the company's main backer and guiding light. Which is nice for him, because MPD owns almost half of the world's richest new diamond mine, Gahcho Kue.

The mine, which is one-third through its construction phase, is located high up in the Canadian tundra, far from the sun-kissed Barbadian beaches of Desmond’s beloved Sandy Lane.

When one considers the prize on offer, however, I bet Gacho Kue is just as close to his heart.

Patrick Evans, MPD's chief executive, told me this week that Gahcho Kue, which is 51 per cent owned by De Beers, will generate net cash flow of about $300 million annually for MPD for at least the first five years of the mine, which will be operational by 2016.

MPD has no other live assets apart from Gahcho Kue, which is also operated by De Beers. That means the cash should flow mostly to the bottom line. Desmond owns almost a quarter of the company.

Even for a billionaire, that’s an enormous chunk of change.