You don't need to ASK for his permission, but you need to let him know mano a mano. It's the decent thing to do. Just because he dated a girl doesn't mean that she's off-limits to all other guys who know him. If religion and the law permits one to marry his brother's ex-wife (whether the brother is alive or dead), then certainly there is nothing wrong with dating a girl your friend once dated. So, you don't have to feel as if you're doing anything wrong. If you had to first seek his consent, then you are devaluing the girl by treating her like a property which requires the consent of its owner before another can make use of it. But this is not the case, so that is why it is inappropriate for you to ask for his permission. But it is also not honourable to be sneaking behind your friend's back, or to surprise him by the fact that you're dating his ex. So, the proper thing to do is to let him know that you and this girl have been getting along lately and you want to ask her out, you just wanted him to hear it from you first since you're friends and he has a past with her. Do not make it sound like you're asking him for permission, because if you do then you are giving him the power to say NO. And I don't think that would stop you anyway (and if it does, then you're a pussy and never deserved her anyway). You are simply INFORMING him out of respect, and not out of obligation. If he doesn't seem too pleased about it, that's none of your business, it's his ego problem he needs to resolve (you know, the "if I can't have her no one should" kinda thing). If he still loves her, that's also none of your business. (If there was any real love between them, they'd still be together). All that matters is this: if he reacts negatively about it, you shouldn't hold him in such high esteem afterward, because what you need are friends who are mature and decent enough to know what is right and what is simply selfishness.