The actress, who played Walford matriarch Peggy Mitchell between 1994 and 2010, predicted that St Clement will be "sorely missed" by EastEnders fans once her final scenes as Pat Evans air over the festive period.
St Clement announced her decision to leave EastEnders back in the summer, explaining that she wished to pursue "other work and life opportunities" after 25 years with the show. Pat's final storyline will see the iconic character pass away following a short period of ill health.
Speaking of the star's EastEnders exit, Windsor today told This Morning: "Oh, I can't bear it - Pam! And she will be sorely missed - more than I was missed in the show, because she could go to anybody - any family she could go into. I am devastated."
"She definitely wanted to leave, but I don't know if she wanted to be killed off - that's the chance you have to take," Windsor continued. "I was positive that I was going to go up in a load of flames with The Vic - I thought that was going to happen, but of course it didn't.
"With Pam, I was very, very surprised, because she could always go back. But she's accepted it now and she'll have a new life."
Windsor also confirmed that she is unlikely to return to her role as Peggy but would not rule out the possibility completely.
Asked whether she would play the character again, she replied: "I don't think so, no. You can't say that - you mustn't say no. I love the show very, very much and my 16 years [there] was the best thing ever. I loved it and I thank them from the bottom of my heart. But I don't know."
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> EastEnders Pam St Clement's exit storyline revealed
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> Read more EastEnders spoilers and news
Watch Pat's EastEnders character trail below: