West Ham boss Sam Allardyce believes Andy Carrollâ€™s spell on loan with the Hammers was crucial in the former Liverpool striker opting to make the move permanent.
"Our relationship over the 12 months he was here was key to this deal," he told the club's official website.
"He came to us in a difficult frame of mind and had suffered with injuries but the support the coaching staff and the rest of the boys that work so hard behind the scenes was something he felt very comfortable with in the end.
"He met new team-mates over the year and enjoyed their company and I think that definitely helped him to make the decision to return to West Ham. So not only did the loan pay off by us finishing 10th in our first season back in the Premier League but it has paid off by him choosing us."