AFP - Actress Sandra Bullock abruptly canceled a planned visit to London for the UK premiere of her movie "The Blind Side" for which she won an Oscar, amid speculation Thursday about her marriage.

Warner Bros studio issued a statement in Bullock's name explaining that "due to unforeseen personal reasons, a trip abroad to support the opening of 'The Blind Side' has been deemed impossible at this time."

"I apologize for any inconvenience this may have caused and thank you for your understanding and continued support of the film," the statement added.

The cancellation came amid reports that Bullock's husband of nearly five years, Jesse James, had an affair while the actress was filming "The Blind Side," for which she won her first Oscar for best actress this month.

James's alleged mistress, a heavily-tattooed model named Michelle "Bombshell" McGee, told US gossip magazine In Touch that she had an 11-month affair with Bullock's husband.

She claimed the pair met up after James responded to her request for information about modelling on his television show "West Coast Choppers."

"He started saying, 'Do you want to hang out?'" and she travelled to Los Angeles to meet him a week later, she said.

McGee said James was ambiguous about his relationship with Bullock.

"We ended up on the couch," she told the magazine. "He wanted to watch movies, but I asked him, 'What's going on with you and Sandra?'"

"He said, 'She doesn't live here. She has a house in Austin. She is filming, and I can't talk about it,'" which McGee said led her to believe the couple was separated.

McGee told the magazine that she and James began sleeping together that night and continued their physical affair for the next five weeks, texting each other several times a day.

Representatives for Bullock declined to comment on the report and James's lawyer could not be reached.

People magazine, another US celebrity gossip publication, reported that Bullock had moved out of the couple's shared home in southern California several days before the In Touch article emerged.

Bullock, 45, and James, 40, met in 2004 on the set of "Monster Garage," a show he presented on the Discovery Channel. They married a year later in July 2005.

The union surprised a number of Hollywood observers because Bullock's reputation for being low-key, discreet and mature contrasted with the bad-boy image cultivated by James.

The tattooed James, a distant relative of the legendary 19th century US outlaw of the same name, had been married twice previously, including to a porn star against whom he fought a series of messy legal battles.

The couple have no children of their own, but care for James's three children from his two previous marriages.

Reports of marital strife came as Bullock celebrated her most successful year yet, receiving a slew of awards for her turn as Leigh Anne Tuohy, a feisty southern matriarch who mentors a troubled teenager, in "The Blind Side."

James accompanied her to a series of publicity and award events, applauding as she swept honor after honor.

At the Golden Globes, she dedicated her best actress win to him.

"There is no surprise that my work got better when I met you because I never knew what it felt like for someone to have my back. So, thank you," she said.