Blackstone, which is led by billionaire Stephen Schwarzman, has taken a near $20m interest in the owner.
An SEC filing shows Blackstone has built up 1,500,000 Ardmore shares to give it a 6% holding.
Ardmore shares last traded at $13.29 apiece, valuing the investment at $19.935m last night.
Blackstone appears to be the second largest outside investor in Ardmore after Donald Smith & Co, which owns 10.1% of the company.
Last month hedge fund Kensico uncovered a 5.4% stake in Ardmore.
Its largest investor overall is private equity fund Greenbriar Equity, controlled by Ardmore chairman Reginald Jones. Its 8,050,000 shares are enough for a holding of 44.6%.
Jones was one of the top shipping investment bankers of his day at Goldman Sachs, leading the Teekay IPO, Teekay’s buy of Bona Shipping and the sale of SeaLand to AP Moller-Maersk, among others
Blackstone is a major investor in shipping with its Eletson Gas joint venture set for an IPO in the US. It also has interests in companies ranging from Brazilian operator CBO to Hafnia Tankers of Denmark.
Schwarzman has a fortune of $10.5bn according to Forbes magazine, making him the 114th richest person on the planet.
