British Airways' and Iberia's shares have been cancelled from the stock exchange after the merged companies began trading today as the International Consolidated Airlines Group.
In early trading the shares stabilised at around £2.85 ($4.55), down slightly on their debut.
IAG chief executive Willie Walsh, outgoing head of BA, is convinced that the move elevates the two partner carriers into the big time and will provide a springboard for even greater things.
"This creates for Europe a third major force in world aviation," says Walsh, who famously revealed last year that he had drawn up a list of potential future partner airlines.
"IAG's strategic ambition is to provide a platform that is attractive to other like-minded airlines to join us," he says.
Assisting Walsh at the helm is former Iberia chief executive, and now IAG chairman, Antonio Vazquez. He sees the link-up as vital to ensure both airlines remain competitive in the long-term.
"Both companies now have the feeling that working together everything is possible, because we have a much broader way of looking at the world," he says.
The Oneworld alliance-aligned group, which began trading on the London and Madrid stock exchanges today, may be a new "superpower" but it can't yet rival Europe's other two giants Air France-KLM and Lufthansa, on paper.
Like Air France and KLM, BA and Iberia continue to operate as separate entities, but their combined traffic - based on last year's World Airline Rankings for fiscal 2009, from ATI sister publication Airline Business - means it is placed sixth behind its two European opponents.
In terms of revenue, IAG lies seventh in the rankings while its fleet of some 340 aircraft puts it eighth. It trails Air France-KLM and Lufthansa on both metrics.
But the merger isn't all about size, points out Vazquez. "We expect to achieve €400 million in annual cost savings by year five through synergies - one third from revenue and two thirds from cost," he says.
There is a good fit between the two airlines' long-haul networks, with BA's strength on the North Atlantic complemented by Iberia's powerful presence between Europe and Latin America. Added to this is the recently awarded anti-trust immunity awarded to Iberia and BA - along with Oneworld partner American Airlines - for their transatlantic business. The partners are already beginning to reap the benefits from this.
There is also some fleet commonality - both carriers fly Airbus A320s on their short-haul network - and this will be further enhanced when IAG uses its buying power to negotiate a huge joint deal for new long-haul types to replace BA's Boeing 747-400s and Iberia's older A340s.
Walsh and a small team of dedicated IAG staff have taken up residency on the edge of London Heathrow, down the road from his old office at BA's Waterside headquarters. Walsh will also have a presence in Madrid, as will Vazquez.
BA's former chief financial officer Keith Williams succeeds Walsh at BA, while Iberia's former chief operating officer Rafael Sánchez-Lozano takes over from Vazquez at the Spanish flag-carrier.