By Monica Chadha BBC News, Mumbai

Khan was keen to appear in the ad

Shah Rukh Khan is starring in a commercial marking 75 years since Lux soap was first manufactured in India.

A spokesman for Hindustan Lever, which makes the soap, said the actor had jumped at the chance to appear.

Many Bollywood women have advertised the soap, but this is the first time a man has lent his name to the brand.

'Vulnerable'

A spokesman for Hindustan Lever, the Indian arm of the multinational Unilever, said the firm had learnt of Shah Rukh Khan's desire to star in a Lux commercial, following in the footsteps of actresses Hema Malini, Juhi Chawla, Madhuri Dixit, Kareena Kapoor and Aishwarya Rai.

They should have let Shah Rukh be himself - naughty and funny Film maker Prahlad Kakkar

"Our advertising agency somehow managed to hear that Shah Rukh had told his co-stars Juhi Chawla and Hema Malini while shooting for a movie that they are the real stars as they get to sit in elaborate bathtubs and advertise for Lux," the spokesman, Paresh Chowdhury, told the BBC.

Film maker Prahlad Kakkar said it was a coup to get Shah Rukh Khan to pose like this in a bathtub.

"The target audience, which is basically women between six and 60, love him because he comes across as vulnerable," he told the BBC. "You could have had some macho actor get in tub but he would seem unreal.

"Shah Rukh Khan is a man with a very strong female side - he is not ashamed of not having any hair on his chest - yet he is a man's man."

Script criticised

But Mr Kakkar said the commercial had not been well made.

"They had a script! They should have let Shah Rukh be himself - naughty, funny - but they had him sitting in the bathtub saying lines according to a script.

"It could have been made better."

Khan is a leading Bollywood actor with more than 50 films to his credit, of which 18 have been hits at the box office.