Should I warn my work colleague?

My work collegue has been asked out by my ex-boyfriend. We broke up a few years ago and I'm now very happy with my lovely new man. I broke up wih my ex as he was very arogant, ist and made me feel very trapped. He didn't take the break-up well and made me feel very guilty about it. My work colleague didn't know him that well when we were going out, but has recently been bumping into him in town and she told me that he asked her out yesterday. Part of me wants to wish her well and stay out of it, but she's a lovely girl and I don't want her to go through what I did. How can I warn her without sounding like a jealous ex (which I'm not in any way!)? Any advice would be fab.