The 83-year-old actress, who famously played Pat Butcher in the BBC soap EastEnders, is making a surprise comeback in a special Christmas episode that will air tonight (December 23.)
Her character appears as a figure in a dream sequence which is part of a storyline exploring Nigel Bates' dementia.
Asked what it was like to reprise the part of Pat, more than a decade after being killed off, Pam said: "Coming back to jump into those clothes and make-up again was strangely difficult.
"I thought it was going to be much easier, but I think I've probably been through the point in my life, having played her, where I had divested myself of her.
"Her accoutrement, her clothes, her make-up and everything else, and I thought I had, but the strange thing is that the public don't because it's so fresh.
"That's probably because there are a lot of repeats that go on, on television, like EastEnders classics and things like that."
St Clement said she was surprised when asked to return.
She said: "I think I was a bit bewildered, and a bit bowled over."
She revealed what helped her rediscover the character after so many years.
She said: "I have to say, to get into Pat's character, is obviously much harder today than we've been filming, but I would say that the key to the whole ensemble must be the earrings."
EastEnders executive producer Ben Wadey described her return as "an honour".
Mr Wadey said: "It's an honour and a privilege to welcome Pam St Clement back to EastEnders for a special episode in Nigel's ongoing dementia storyline.
"Pat Evans is one of the most cherished and iconic characters to have graced the streets of Walford, and I know I speak on behalf of everyone when I say what a delight it was to see Pat and Pam back in The Queen Vic as she helps Nigel in his time of need."