John Obi Mikel has joined Middlesbrough on a short-term deal, the Championship club have confirmed.
The 31-year-old has finalised his move to the Riverside Stadium after leaving Chinese side Tianjin Teda at the end of the Super League season in November.
Mikel is Boro's second signing this month, following the loan arrival of Rajiv van La Parra from Huddersfield Town.
The midfielder spent 11 years in England with Chelsea, winning two Premier League titles, three FA Cups, the EFL Cup, the Europa League and the Champions League.
The Nigeria international, who played at last year's World Cup, had been linked with moves to Ligue 1 and the Bundesliga, as well as Saudi Arabian side Al Nassr, before agreeing to sign for Boro.
Tony Pulis' side sit fifth in the Championship table after 28 matches, seven points behind leaders Leeds United.