Royal Caribbean (RCCL) is expecting "significant synergies" after agreeing to take a $1bn controlling stake in luxury and expedition cruiseship company Silversea Cruises.

The US giant said the deal for a 66.7% holding will propel the growth of the brand.

The move was announced by RCCL and Silversea chairman and owner Manfredi Lefebvre D'Ovidio.

It brings together two companies with "bold, long-term visions for the cruise industry," they said.

The takeover is being financed with debt.

Florida-based Silversea has nine operational vessels, with two more due from Fincantieri in 2020 and 2021.

Lefebvre will qualify for an estimated 472,000 RCCL shares worth $51m, payable upon achievement of certain 2019-2020 performance targets.

"Silversea is a crown jewel, and the acknowledged leader in luxury and expedition cruising, two key markets that are poised for growth," said Richard Fain, chairman and CEO of RCCL.

"We are proud to welcome aboard Manfredi Lefebvre, a visionary leader whose high standards and history of innovation we deeply respect. Manfredi will remain executive chairman of Silversea, continuing to lead its strategy long term."

"This partnership will bolster the growth of this exceptional brand founded by my father," said Lefebvre.

"Kindred spirits"

"I have always been kindred spirits with Richard and we share a vision of offering excellence and leadership to our guests. This new partnership gives Silversea the opportunity to accelerate the growth of the most successful luxury and expedition cruising brand in the world."

The companies aim to drive long-term capacity growth in the burgeoning sector at a much larger scale than Silversea would achieve independently, they said.

Savings will be made in areas like global market access, the supply chain, purchasing power and other economies of scale.

Lefebvre said he is confident that the significant investment stake he is retaining will sizeably increase its value through the growth the long-term partnership will enable.

Lefebvre and Fain also confirmed that Silversea's CEO Roberto Martinoli will continue in his role, working with the existing Silversea management team.

The deal should close later in the year, subject to regulatory approvals.