Fernando Torres says it was his decision to leave Chelsea and claims a return to Atletico Madrid was never discussed.
Kurt Zouma says he is 'very happy' to be at Chelsea, with a lot being learned despite his limited game time.
The 22-year-old only featured twice for the Swans after his move from Arsenal last summer, spending more than three months on the sidelines with a thigh injury.
His chances of regular playing time this season were not helped by the recent signing of Espanol centre-back Jordi Amat and Swansea have opted to send him out on loan to gain more first-team experience.
Bartley was regularly loaned out when he was with Arsenal, having two spells with Sheffield United and Rangers.
"It's great news. As soon as my agent mentioned the move then I was all for it because this is a massive club with a massive fan base. I know the manager well and he's a really good young manager who matches the club's ambition," Bartley told the club's official website.