Chelsea have completed a loan deal for Manchester United forward Jadon Sancho.
The deal is understood to include an obligation to buy if certain thresholds are met.
In a separate deal, also concluded late on Deadline Day, Chelsea have loaned Raheem Sterling to Arsenal.
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Sancho has scored 12 goals and contributed six assists in 83 games for United since signing from Dortmund for £73m three years ago.
Sancho - who has 23 caps for England - fell out of favour at United last season after a public disagreement with Ten Hag.
The forward was welcomed back into Ten Hag's squad this summer but his only action so far this season was a brief appearance from the bench in the Community Shield.
Chelsea back 'opportunistic' Sancho signing
Sky Sports News chief reporter Kaveh Solhekol:
"Some Chelsea fans will be thinking whether they really need to sign Jadon Sancho, with the club having already signed wingers like Pedro Neto and Joao Felix this summer, with Cole Palmer and Noni Madueke already at the club, and with Sancho not appearing to be in Erik ten Hag's plans at Manchester United.
"I think the reason Chelsea are going for him is that it's an opportunistic move. Sancho would be available for a sensible fee and, on his day, he's a very good player - he played in the Champions League final for Borussia Dortmund in June, and three years ago he was an £85m player."
Analysis: Could Sancho shine at Chelsea?
Sky Sports' Nick Wright:
Jadon Sancho is still only 24 but he has work to do to put his career back on an upward trajectory and prove he can still fulfil his considerable potential.
He was seen as one of the best young players in Europe when swapping Manchester City for Borussia Dortmund as a teenager. His first full season in Germany brought 12 goals and 14 assists in league games alone. He followed it up with 17 goals and 16 assists in his second.
But it is four years since those incredible highs. His output dipped in the subsequent season at Dortmund and his move to Manchester United, completed in the summer of 2020, has brought frustration. Even last season's loan spell back at Dortmund felt underwhelming.
His minutes have decreased in each of the last six seasons - his goals and assists have followed a similar pattern - and the move to Chelsea follows a false dawn at United, with Sancho unused this term despite an apparent reconciliation with Erik ten Hag.
Staying at Manchester United was unlikely to bring a change of fortunes but Chelsea present challenges too. Sancho needs to play but, even with Raheem Sterling loaned out to Arsenal, Enzo Maresca already has a large cohort of wide forwards.
Cole Palmer, Sancho's former City academy team-mate, is surely an immovable presence in Chelsea's forward line. The Blues have also added Joao Felix and Pedro Neto to a unit which already includes Christopher Nkunku, Noni Madueke and Mykhailo Mudryk.
It is hard to see where Sancho fits. Swapping Old Trafford for Stamford Bridge is a fresh start. Whether the circumstances are right for him to shine again is less clear.