Jill Demirel, 38, claims she and married dad-of-two Alex Walkinshaw shared explicit texts after they met while dropping their children off at drama school.
Speaking with the Sunday People, the former glamour model claims that Walkinshaw, 39, who plays heartthrob staff nurse Adrian “Fletch” Fletcher in the BBC drama, repeatedly requested topless photographs during their late night exchanges.
Jill said: “It was all quite innocent to start with. He would text during the week and kept saying we should meet up for a coffee or a chat. I thought he simply meant as friends.
“Then [...] he began following me on Twitter and sent me a private message, telling me I looked gorgeous.
“He told me he was filming in Cardiff and was feeling really lonely. He started texting me in the middle of the night, asking what I was up to."
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She added: "He said he was lonely and then he asked if I could send him some text messages to excite him.
"He then kept asking me to meet him. It was clear what he wanted.”
Jill, who was last year chosen by Ann Summers to design a range of sex toys for a TV documentary, went on: “It was really awkward. I knew he was married and he knew I was married.
“He told me I had nice breasts and, yes, I did send him a picture of my boobs while they were in my bra. He asked me, ‘When can we meet?’ He kept saying that he wanted to meet up until a month or so ago.
“I’ve met him but I haven’t actually had sex with him. My husband found the messages on my phone and went mad.”
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Last month, Walkinshaw revealed that he moved from Casualty to Holby City because it was closer to his family.
In an interview he said: “I was struggling with being so far from home. It was too hard on my family. They came up with the idea to transfer Fletch and move me to Elstree.
“Casualty was filmed in Cardiff and I live in Kent. It’s a long way away when you’re doing five days a week.”
He has yet to respond to the claims made by Jill Demirel, although a source said yesterday: “Alex admits he exchanged messages with this woman but he never met her for sex.
"He never would have because he loves his wife.”