Star Breeze debuted its new look in June, sporting new suites and expanded outdoor and indoor public spaces.
On Monday (27 September), Star Legend returned to service in Lisbon after works at the Fincantieri shipyard.
It is currently sailing a 10-night Barcelona voyage with calls in Portimao, Cadiz, Gibraltar, Malaga, Cartagena and Palma.
Windstar said the "stretch and transformation project" would increase onboard capacity from 212 to 312 guests.
The ships have also been fitted with what Windstar claims to be more efficient engines, generators and advanced wastewater treatment systems.