Ryan Goodman, 19, had fought with twin Michael in February last year after their mother shouted at them over money that had gone missing from her purse.
The twins, believed to originally be from Northampton, blamed each other for stealing the money.
Terrified on seeing his brother had no pulse, Ryan dragged Michael’s body out of the family’s country villa near Valencia, an area popular with ex-pats.
He hid the body beneath undergrowth in a ditch just ten metres from their front door.
Michael’s decomposed body was only found in April this year when a wild asparagus picker stumbled across the remains. DNA testing confirmed his identity.
The twins’ mother Lynette, 39, had only reported her son missing three months after he vanished.
It is believed Ryan had told the family his brother had returned to England and they did not raise the alarm as he was ‘prone to disappear’ for weeks at a time.
Police had questioned Ryan and his grandfather David, 62, several times about Michael’s disappearance, believing Mr Goodman was covering for his grandson, local reports said.
Appearing at court in the nearby town of Xativa last week, Ryan told the investigating judge that it had been an accident and he was very sorry:
‘I loved my brother and had no intention of killing him,’ he said, adding that he had hidden the body because he was ‘very scared’ of the consequences.
The judge remanded him to the custody of youth criminal services because he had been 17 years old when the crime was committed.
He will spend six months in a juvenile detention centre while he awaits trial.