Under-fire actress Kristen Stewart was noticeably absent from the red carpet at the premiere of her new film On The Road in London on Thursday night (16Aug12).

The film's male stars - Sam Riley, Tom Sturridge and Danny Morgan - attended the glitzy event at the British capital's Somerset House without their leading lady, after she decided not to fly to the U.K. to help promote the movie.

Stewart hit headlines last month (Jul12) when she admitted to an "indiscretion" with married director Rupert Sanders behind the back of her boyfriend and Twilight co-star Robert Pattinson and she has been lying low ever since.

When asked about Stewart's absence from the premiere, her co-star Morgan said the actress was upset she wasn't able to attend, telling website Heatworld.com, "It's a shame. We would have all loved her to be here and it would've been great and I know she's sad she can't be here.

"She would've loved to be here because I know she's so proud of this film and her performance in it and she's amazing in it. People will be blown away by it. She's incredible."

Stewart will reportedly return to the spotlight when On The Road is showcased at the Toronto International Film Festival in Canada next month (Sep12).