Denis O'Brien has increased his interest in Independent News and Media to 29.9%, the maximum allowed before triggering a takeover bid.
The announcement was made in a regulatory filing to the Irish Stock Exchange.
This is the maximum that he can own without triggering a full bid for the company.
A spokesman for Mr O'Brien confirmed the purchase had taken place, but declined to speculate on what Mr O'Brien's future intentions are.
Mr O'Brien increased his stake by buying a further 10.6 million shares today, through three separate investment vehicles. At today's current share price, the total value of the transaction would be €3 million euro.
Shares in the company were down 6.62% at €0.30 a share a short time ago but were up over 16% in trading over the last seven days.
This follows yesterday's move to purchase of 5% of the company.
It's believed Denis O'Brien had invested upwards of €500m in shares in Independent news and media up to this.
The billionaire businessman is already the largest shareholder in the media group and last month saw Gavin O'Reilly step down as chief executive - the terms of that exit now itself the subject of a court action.
