Qatar Airways Group says it had increased its stake in Aer Lingus-owner IAG to 25.1%.
The company said its investment in the British aviation group, which also owns British Airways and Iberia, had been highly successful and it continued to support the group and its strategy.
Qatar previously held 21.4% of IAG.
"Qatar Airways continues to consider opportunities to invest in airlines and support management teams that share our vision to enhance travel opportunities for airline passengers across the globe," said Qatar Airways group chief executive Akbar Al Baker in a statement.
The cost to Qatar Airways of increasing its IAG holding is £465 millionn, based on the closing price of IAG's shares yesterday.
Qatar first invested in IAG in 2015, buying 9.99% of the company, and has steadily increased it since then.
It also owns stakes in China Southern and Cathay Pacific, and said earlier this month it was in talks about doubling its holding in LATAM Airlines Group to 20% and buying a 49% stake in Africa's RwandAir.