Oh, I like that. I'll admit that my mind mostly tends to work in embarrassingly vanilla ways, so I never really think of that kind of stuff, but I could definitely see it going like this.
I'm not sure how much Ianto knows about Jack, which would depend on how much Jack and whatever he did in Cardiff after he took over was talked about in London and on how completely he wiped the traces of his TW Cardiff past, but I'm pretty sure that Ianto is the only one who knows where, or at least with whom Jack went when he left, especially if he talked to Gwen and she happened to mention the 'the right Doctor' thing. Not that this makes it any easier for him of course, because unlike Gwen, whom he doesn't even seem to see as a rival, this is someone he can't really compete with, or at least that's how it must look to him.
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I'm not sure how much Ianto knows about Jack, which would depend on how much Jack and whatever he did in Cardiff after he took over was talked about in London and on how completely he wiped the traces of his TW Cardiff past, but I'm pretty sure that Ianto is the only one who knows where, or at least with whom Jack went when he left, especially if he talked to Gwen and she happened to mention the 'the right Doctor' thing. Not that this makes it any easier for him of course, because unlike Gwen, whom he doesn't even seem to see as a rival, this is someone he can't really compete with, or at least that's how it must look to him.