|Port of registry:|
|General characteristics (as Ocean Princess)|
|Class and type:|
|Length:||181.00 m (593 ft 10 in)|
|Beam:||25.46 m (83 ft 6 in)|
|Draught:||5.80 m (19 ft 0 in)|
|Decks:||11 (9 passenger accessible)|
|Speed:||18 knots (33 km/h; 21 mph)|
Sirena, formerly R Four, Tahitian Princess, and Ocean Princess is an R-class cruise ship formerly owned by Princess Cruises. When part of the Princess fleet, along with the Pacific Princess, Ocean Princess was one of the two smallest in the fleet. In March 2016, she was sold to Oceania Cruises and renamed Sirena.
The vessel entered operation in 1999 under the flag of Renaissance Cruises. The ship was not owned by the company; instead she was owned by a group of French investors. When Renaissance declared bankruptcy in 2001, the ship was seized by creditors, along with the other seven vessels in the fleet.
In 2002, Princess Cruises secured a two-year lease for R Four and her sister ship R Three (now Pacific Princess). The vessel entered operation at the end of 2002, and was renamed Tahitian Princess. At the end of the lease, Princess Cruises purchased both vessels.
In November 2009 the Tahitian Princess was renamed Ocean Princess to "reflect a more global theme."
It was announced on November 25, 2014, that the ship was to be sold to Oceania Cruises for $82 million under a finance agreement. She departed the Princess fleet in March 2016 and underwent a 35-day, $40 million refurbishment in Marseille, France to become Sirena.  On April 27, 2016, The Sirena was christened and entered service for Oceania.
MS Sirena is scheduled to undergo a significant renovation in May 2019 as a part of the company's $100 million OceaniaNEXT program.
- Asklander, Micke. "M/S R Four (1999)". Fakta om Fartyg (in Swedish). Retrieved 12 August 2010.
- Ward, Douglas (2006). Complete Guide to Cruising & Cruise Ships. Singapore: Berlitz. pp. 609–610. ISBN 981-246-739-4.
- "Tahitian Princess Deck Plans". Princess Cruises. Archived from the original on 16 July 2011. Retrieved 12 August 2010.
- "Tahitian Princess to be renamed Ocean Princess to reflect better new deployments". Cruise Business Review. Cruise Media Oy Ltd. 4 April 2008. Retrieved 12 August 2010.[dead link]
- "Carnival Corp. Provided Financing on Sirena Ship Transfer to NCLH". 2016-03-16. Retrieved 2016-03-18.
- "Oceania Cruises Remodeling Every Stateroom on Their Four Cruise Ships". cruisefever.net. Retrieved 2018-08-14.