The Good Girl Gone Bad singer, who makes her acting debut in Peter Berg’s action adventure, donned an olive-green silk Grecian-style dress and pointed court shoes for a photocall with co-stars Taylor Kitsch and Brooklyn Decker.
Brooklyn, meanwhile, opted for a more daring monochrome dress with revealing cut-out panels.
Rihanna, 24, told reporters she was single after bristling at being probed about her private life. “I’m happy and I’m single,” she said.
The Barbadian star plays Petty Officer Cora Raikes in the new movie which pits the US Navy in a battle against alien invaders.
“My dad used to make me sit outside on the steps all night long looking for a UFO flying by and I really used to do that for years,” she said. But she was unable to spot anything suspicious. “I saw a falling star once and I thought, ‘yesss dad come and see one’ – it just darted.”
The Corinthia Hotel event comes after Rihanna was spotted using the London Underground to get to the capital’s 02 Arena, to watch rapper friend Drake perform.
The star – recently been linked to Two And Half Men’s Ashton Kutcher – went for a raunchier look for the gig, in a flame-printed T-shirt, cut-off denim shorts and thigh-high leather boots.
Rihanna has used public transport before to get to the venue – she took the Tube to a Brit awards rehearsal last month, and last October made her own way to her O2 concert surrounded by commuters.