Devastated Australian movie star Liam Hemsworth has shocked those close to him by cancelling a promotional event for his new film following the dramatic split from pop star wife Miley Cyrus.

Hemsworth was due to be the star attraction in a press junket and premiere screening of the indie action thriller Killerman in Los Angeles next week, but has been too "rocked" by the breakup to attend, sources told the Daily Mail.

The star of the Hunger Games franchise had told executives back in May that he was "on board to get the movie going", happy that he had put in his best performance in recent years, news.com.au reports.

Movie execs had even planned for a "real Hollywood affair" that would have seen Cyrus joining Hemsworth for the premiere as well as A-list friends and family.

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But in the past few weeks, the Australian reportedly went missing in action as he battled to save his 10-month marriage to Cyrus.

Friends of the actor, who has been holed up in Byron Bay since the split, revealed he can't face heading back to his Los Angeles home with Cyrus, who was spotted with Brody Jenner's ex Kaitlynn Carter in LA, days after the two were photographed kissing in Lake Como, Italy.

Meanwhile, Jenner came out in defence of Carter on Instagram, saying the pair continued to be "best friends" and that there was "too much negativity" being directed at her.

"I respect Kaitlynn and care deeply about her," Jenner said.

A business associate told The Mail Liam has been "so rocked" by the split that he cannot get his head around focusing on work.

"He is not coming to LA for Killerman anymore even though he had told the film executives that he loved the movie and wanted to go full force into promoting it," the insider said.

"There was a feeling that the premiere was going to be a major summer event with Miley joining her husband. All the signs and talk from his team was that Miley and he wanted to put on a public show of support.

"There was even a plan for Liam to appear on the late night talk shows to promote the film.

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"He is deeply upset that things did not work out and stunned at seeing how quickly Miley appears to moved on.

"He is now not in the right head space to step back into the limelight to do any promotion as he knows Miley's name will come up.

"Liam is just surrounding himself with close family to try and heal and see what Miley does next. They want him to stay at home and heal.

"Even the thought of jetting back to LA is painful for him."

The couple have a Malibu home, to which Cyrus has returned with Kaitlynn Carter.