I have a character who moved from Spain to London at the age of four, with his Spanish parents. At this point he knew virtually no English, but was sent to an English primary school soon afterwards. At home, his family continued to speak Spanish. My questions are, how quickly would he become fluent in English? How fast would his accent fade? How much Spanish would he retain as an adult (not having been in contact with his family since he was a teen)? Would any of his accent last into adulthood?