The new ships, says Princess, will be the line’s most environmentally friendly to date, powered primarily by LNG to reduce emissions.

Each ship will weigh in at 175,000 gross tonnes and will be able to accommodate around 4,300 passengers - the largest, by capacity, in the Princess fleet.

They will be built by Fincantieri in Italy for delivery in late 2023 and spring 2025.

Jan Swartz, president of Princess Cruises, said: “This revolutionary platform for next-generation, LNG-powered cruise ships will introduce innovative design and leisure experiences driven by the future holiday and lifestyle trends of our guests.”

Giuseppe Bono, Fincantieri chief executive, added: “We are proud to extend our long-established partnership with Princess Cruises. After so many years, we are ready to enter a new era of this industry, increasingly aimed at reducing even more of our environmental impact. We proudly do this with an all-time record project, both in terms of size and technology.”

Further specs of the two new ships will be released at a later date, Princess has said.

Princess already has three Royal-class ships on order with Fincantieri, including its next ship Sky Princess, scheduled for delivery in October 2019.

The other two will follow in 2020 and 2022.