Millen finally snapped up the England Under-21 international from Tottenham in a loan deal on Thursday, and admits it has been a long wait.
He told the club's official website: "We tracked Danny throughout last season and even the year before that. He's one we've been keeping an eye on for a very long time. I told him this has been a man-hunt!"
Millen stayed in close contact with Spurs boss Harry Redknapp, speaking to him nearly every day, but was still a little shocked when Redknapp finally gave the green light for the deal to go ahead.
"I spoke to Harry on Monday and I must have caught him on a good day because he agreed that it was the right time for Danny to go out on loan and get some match action," he added.