Watford have confirmed the signing of Nathaniel Chalobah on a five-year deal from Chelsea.
Sky sources understand that the fee for the 22-year-old is an initial £5m that could rise to £7m.
Chalobah returns to Vicarage Road having made 42 appearances while on loan in the 2012-13 season, where he scored five goals.
The England U21 international midfielder, who will wear No 14 for the Hornets, made 15 appearances last season as Chelsea won the Premier League title.
However, he had less than 12 months remaining on his contract and his chances of playing a key role for the Blues in their forthcoming campaign could have been further reduced as they close in on the signing of midfielder Tiemoue Bakayoko from Monaco.
He has also had loan spells with Nottingham Forest, Middlesbrough, Burnley, Reading and Napoli in the past.