The Rocky Horror Show, written by Richard O'Brien in 1973, has been seen by over 20 million people in more than 30 countries

The Rocky Horror Show writer Richard O'Brien is living up to his creation Frank N Furter, who sang "I'm just a sweet transvestite from Transexual, Transylvania."

The 70-year-old actor and writer told the BBC that he thinks of himself as 70% male and 30% female.

However, for many years, O'Brien says he was ashamed about his secret desire to be more feminine.

"I was six-and-a-half and I said to my big brother that I wanted to be the fairy princess when I grew up. The look of disdain on his face made me pull down the shutters. I knew that I should never ever say that out loud again," he said.

For half a century, O'Brien repressed the feeling. But "you can't just put the lid on things and pretend that they don't exist", he says.

Around ten years ago, he started taking the female hormone oestrogen - and is satisfied with the results.

"It takes the edge off the masculine, testosterone-driven side of me and I like that very much. I think I've become a nicer person in some ways, slightly softer. For the first time in my life, I've started to put on a little bit of weight, which I like."

The Crystal Maze presenter revealed that he has developed small breasts, but is not intending to have sex reassignment surgery.

The 70-year-old has spoken about his struggles with assigned gender roles and describes himself as transgender or possibly third sex.

"It's my belief that we are on a continuum between male and female. There are people who are hardwired male and there are people who are hardwired female, but most of us are on that continuum and I believe myself probably to be about 70% male, 30% female."

In a Guardian interview, the twice married father of three, said: "Being transgender is a kind of curse. I've been confused about it all my life, and I suppose it's made me a bit of a loner. Thankfully, in the past few years I've allowed myself to give in to it and enjoy life."

The Rocky Horror Show is the longest-running theatrical release in film history, and has made more than $100 million (£63m) worldwide since its release.

It is marking its 40th anniversary this year, with a new production which will tour throughout the UK in 2013.

When asked which box he ticks on his passport, stating male or female status, O'Brien says, "I tick the M. But I would quite like to have other to tick."