Seven Seas Explorer: the most expensive, luxurious cruise ship ever built

It was a big day for cruise fans and royal watchers alike in Monaco as the tiny country's Princess Charlene christened what is billed as the most luxurious ship ever.

Accompanied by her husband and Monaco's reigning monarch, Prince Albert II, the former Olympic swimmer cut a red velvet ribbon to send a primat of Veuve Clicquot champagne crashing against the hull of luxury line Regent's new Seven Seas Explorer.

Costing more than $US450 million ($592 million), Explorer is the most expensive luxury vessel ever built and boasts one of the highest ratios of space-to-passengers in the history of cruising.

Built at a shipyard in Italy, it features some of the largest, most elaborate accommodations at sea, including a two-bedroom complex overlooking the bow of the ship that measures 4443 square feet (413 sq m). That's more than 50 per cent larger than the average American house.

Explorer also has a wide range of upscale eateries including new-for-the-line contemporary French and Asian restaurants, and a newly designed version of Regent's signature steakhouse, Prime 7. A stylish spa operated by Arizona's Canyon Ranch; a two-tiered, 694-seat theatre; and an opulent observation lounge that evokes the 1920s are other notable features.

In a speech during the event, the CEO of Regent's parent company, Norwegian Cruise Line Holdings, Frank Del Rio, said Monaco was the perfect setting for the christening of such a ship.

"This place, famed over decades for glitz and glamour, epic auto races, legendary casinos, a place where dreams come true, where 007 himself orders his martinis shaken not stirred ... can now add the christening of Explorer to her long list of accolades," Del Rio said.

Explorer is Regent's first new ship in more than a decade. It initially will sail in the Mediterranean, offering a range of eight- to 14-night sailings starting at $US6799 ($8954) per person. It will re-position to the Caribbean for the Northern winter.