A youth international with England, the striker has been a regular for Chelsea's Under 21s since he was 15 years old.
A native of South Yorkshire, he spent time as a youngster with Rotherham United before being snapped up by Premier League giants Chelsea in 2010.
Speaking to Barnsley Player, Alex said, "I'm really glad to be here. I'm really looking forward to see what's in store.
"I know a couple of the lads. I've played with Ross (Turnbull) and I know Mason (Holgate), they're a great set of lads and I'm looking forward to playing with them.
"It was number one as soon as they came in. Danny Wilson - the perfect Manager and it's the perfect time.
"I'm young, I want to express myself and show what I can do. I'm quick and I like movement and to get in behind to score goals, so hopefully it'll show."
The striker teams up with the Reds from today, but isn't registered in time to face Middlesbrough this afternoon.
