The European Commission has cleared Carnival's £3.31 billion takeover bid for P&O Princess Cruises.
The decision deals a blow to Royal Caribbean's rival £2.22 billion offer.
Although Royal Caribbean was offering less, it had argued its bid stood a better chance of winning regulatory approval.
Carnival and Royal Caribbean, which are both based in Miami, are numbers one and two in the cruise market. London-based P&O Princess Cruises is in third place.
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Both bids are still undergoing anti-trust review in the United States.
Royal Caribbean had lobbied hard to get the EC to force Carnival to sell off its prized British subsidiary, Cunard Line, but the commission has placed no conditions on its approval.
PA