The businessman Denis O'Brien has bought 2.1% of Aer Lingus for over €32 million.
In a statement to RTÉ News, he said he had purchased the shares in the airline because he believed in competition and because Aer Lingus was a company with a strong national and international reputation.
Mr O'Brien said he has agreed to support the pilots and the staff and the board and management of the company.
Aer Lingus pilots bought more shares in the airline today in an attempt to block Ryanair's hostile takeover.
They bought 300,000 shares at €2.90 per share, spending €870,000.
This latest purchase of shares brings the stake held by pilots to 2.24%.
Concerns over use of pension fund
The Pensions Board has contacted trustees in an Aer Lingus pilots' pension fund and raised concerns about the fund buying shares.
The concern is that the pilots' strategy of buying shares to block Ryanair's bid could reduce the Aer Lingus share price.
That could result in a loss on the investment for the pension fund and its pensioners.
The trustees of the pilots' fund have been told they have a duty to act in the best financial interest of members.