Now 18 years of age, Andrade passed a medical on Friday, arriving back at the club that he departed in 2007.
Benfica were crowned Portuguese champions last season, and Andrade hopes his goals can fire the club to yet more glory in 2014-15.
"I was 12 at the time and very young," he said of his first spell in Portugal.
"I came here alone and cried every night. Santos made a proposal that allowed me to be closer to my family.
"I'm older, more mature and have returned to Benfica. In the end everything went all right.
"I'll get on the field and give my best, the goals will come naturally."
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