OMG...I would never notify the ex-boss. First of all, it's not your position to do charity work. Notifying the ex-boss is. Then, you're putting your coworker in

OMG...I would never notify the ex-boss. First of all, it's not your position to do charity work. Notifying the ex-boss is. Then, you're putting your coworker in an unfavorable position because you don't know that he's truly going to accept your offer. If he accepts the offer and retracts it, how do you think it'd make him look to his employer? and it's not your position to tell his boss that!!