The 19 year old impressed while on trail with the Millers last season, but boss Paul Warne had to wait until this summer to be able to sign him.
The striker is a work in progress signing, but he's hoping to bring him on after signing a 1 year deal today.
Warne gave his thoughts to the clubs official site.
"We had him in for a couple of games last season and he did well, I really liked him as a kid and I still do. He spoke to me a few times about how we can improve him and what we can do and his attitude was spot on. He has got the raw materials but we will have to do a lot of work with him."
"He's come back in good shape. As I speak, seven lads have done the running and he's been the quickest of them, so that always puts him in good stead with me.
"It's another option for us. Julien can play anywhere across the front three or anywhere in midfield so hopefully with a bit of work, he'll turn into what we want him to be."
"I think he's still a development project and in fairness to him, it is some step from where he's come. Even just having full-time training is going to take it's toll on him.
"As I stand here talking to you now, I expect great things for him, but I don't expect him to start the first game of the season. That said, who knows. Sometimes the opportunity comes for you when you least expect it and if he performs to the level we hope he can then I'm not afraid to throw him in.
"I do forsee him playing a part this year but if you asked me to name my eleven now, he probably wouldn't be in it, but that doesn't mean he won't be."
"He's a loveable kid and he can't stop smiling. Certain people work at this club and they work because of how we are as a staff and he is definitely one of those. He is perfect for us in that respect."