Dame Helen Mirren used to lock herself in the toilet because of her nerves about acting.
The 74-year-old actress has admitted she finds her work "incredibly intimidating" and has often hidden away to give herself a pep talk ahead of the start of a new role.
In a new campaign video from the Prince's Trust and L'Oreal for International Women's Day, Helen and a number of other famous females - including Spice Girl Geri Horner, athlete Denise Lewis, and models Iskra Lawrence and Neelam Gill - opened up about self-worth to special women in their lives.
Helen told make-up artist Val Garland: "Many actors exude confidence, I find it incredibly intimidating.
"More than once I've had to run away and lock myself in the lavatory, just to say, 'Come on, you can do this Helen.'
"But before that happens, you're sitting in the make-up and you're very lucky if you're, say, in Val Garland's makeup chair."
The 'Red' actress admitted people are often "surprised" by her insecurities.
Helen said of the 'Self Worth, Worth Sharing' campaign: "[This] is so important for the emotional well-being of young women. I have experienced insecurities all my life, and to many people's surprise continue to do so.
"In today's digital age, social pressure is on the rise, therefore having the right support is more important now than ever."
Helen recently recalled an awkward afternoon when she was invited to tea with Queen Elizabeth - who she portrayed in 2006 movie 'The Queen' - and didn't realise until she arrived that it was an intimate event.
She said: "I thought it was going to be in a room with 200 other people, which it often is. I've met her once before and it was in a room with 200 other people...
"So I walk in, and there's like eight people sitting around a table. Prince Philip, the Queen, a Sheik of somewhere or other and a couple of horsey people. I know absolutely nothing about horses, at all, and the Queen knows everything about horses."
The actress struggled to fit in with the chat.
She said: "I was desperately trying to make polite conversation and it's just coming out like gobbledygook".
And things quickly began to spiral out of control for the Oscar-winning actress.
She continued: "The milk is on the other side of Prince Philip and I want some milk in my tea, but my brain goes completely dead and I cannot remember how to address Prince Philip.
"I mean, is it sir? Is it your majesty? Is it your highness? Is it rude to ask him to pass the milk? Or should I just ask for a lackey? I finished up not having any milk. I just couldn't sort it out.
"It's a lesson in embarrassment, but they were lovely, they were utterly gracious."