Hong Kong's Kingboard Chemical Holdings on Monday said it had agreed to sell its 9.6 percent stake in Cathay Pacific Airways to Middle Eastern carrier Qatar Airways for HK$5.16 billion ($661 million).
Kingboard, an investment holding company, said it would recognise a gain of HK$800 million on the sale which represented its entire stake in the Hong Kong airline.
Cathay shares have risen by 29.4 percent since the start of January despite the airline in August posting its worst first-half loss in 20 years.
The Hong Kong airline has a highly concentrated share register with Swire Pacific owning 45 percent and Air China holding 30 percent.
This is not the first time Qatar Airways has taken a stake in another airline. The carrier owns 20 percent of International Consolidated Airlines Group, the parent of British Airways, as well as 10 percent of South America's LATAM Airlines Group and 49 percent of Italy's Meridiana.
Qatar Airways and Cathay are both members of the oneworld alliance, as is British Airways and LATAM.
The Qatari carrier in August dropped plans to build a stake of up to 4.75 percent in American Airlines Group.
Those investment plans were met with suspicion by critics at a time when Qatar is embroiled in the region's worst diplomatic crisis in years and is locked in an airspace rights dispute with three other Gulf states.