Alberto will be the third new arrival at Anfield this summer following the captures of Kolo Toure on a free transfer and Celta Vigo's Iago Aspas, who will complete a move once all paperwork goes through.
The youngster spent last season on loan at Barcelona B and netted 11 goals.
But he admits it will be a wrench to leave his hometown club Sevilla.
Alberto added: "I've always said that this is the club where I grew up, it's my home.
"I owe a lot to Sevilla, although I'm leaving a little hurt because I haven't had the chance to show what I can do in the Primera Division.
"I've had to take a difficult and important decision and I hope I've got it right."