I'm not gay! (then don't act like you are)

Fed up with mounting speculation about his sexuality, Silverchair frontman Daniel Johns has set the record straight.

The bleach-blonde rocker told Melbourne's Big Day Out that despite rumours, he wasn't a homosexual.

"I'm not f***ing gay," he told the 45,000 strong crowd as he adjusted the lacy garter he wore on stage.

Speculation about the 28-year-old's sexuality intensified earlier this month when he announced he and former Neighbours star Natalie Imbruglia had split.

Meanwhile, a visibly happy Imbruglia stepped out in London overnight to celebrate her 33rd birthday.

The songbird emerged from a restaurant, smiling for waiting paparazzi as she held a giant bunch of roses and a Hermes handbag.

Imbruglia returned to London in early January after a trip to Sydney, where she was seen spending time with Johns.

The couple announced they were ending their marriage of four years several days later.

They cited career demands as the reason for their split.

This mutual decision has not been taken lightly or quickly," the pair said in a joint statement.

"However … our lives in different parts of the world have brought us to the point where unfortunately this difficult decision was necessary for both of us.

"We have simply grown apart through not being able to spend enough time together."