Eoin Morgan has replaced the out-of-form Alastair Cook as England's World Cup captain, the England and Wales Cricket Board (ECB) announced on Saturday.
Cook has scored just one fifty in his last 22 one-day innings for England and has paid the price for failing to stop the rot during his country's recent 5-2 series defeat in Sri Lanka.
Morgan will lead the side for the tri-series in Australia after Christmas and then the World Cup in Australia and New Zealand in February and March, with Cook playing no part but staying on as Test captain.
An ECB statement read: "ECB today (Saturday) announced that Eoin Morgan has replaced Alastair Cook as England one-day captain with immediate effect.
"Selectors recommended to managing director England cricket Paul Downton a change in captaincy, which has now been approved by the ECB chairman. Cook will continue as England Test captain."
After England's series-ending defeat in Colombo on Tuesday, Cook, who has not scored a one-day century since June 2012, conceded he could have "no complaints" if he lost the one-day captaincy.
But the decision to remove him from the role with the World Cup looming is still a major reversal by Downton and head coach Peter Moores, who have given Cook absolute backing this year.
Cook, who turns 30 on Thursday, said: "I am gutted to be left out of the World Cup squad, and it is likely to take me a while to get over the disappointment.
"That said, I wish Peter, Eoin and the lads all the best for the World Cup. I would also like to thank all the players and fans who have supported me during my time as one-day captain."
Morgan described being handed the captaincy as "a huge honour".
The 28-year-old Irishman added: "I firmly believe that with the players currently involved in the one-day set-up we have the makings of a very good one-day side, a young side that can surprise people at the World Cup."
- Ballance selected -
Morgan's elevation to the captaincy represents a U-turn by the ECB, which had cited the need to give Cook full support as one of the reasons behind its decision to end Kevin Pietersen's England career earlier this year.
But Downton said he had "complete confidence" in the decision made by the selectors.
"Having spent time with Alastair yesterday (Friday), he accepts that it has been made in the best interests of the one-day side," he said.
"Eoin has held a senior role in our limited-overs teams for some time and has impressed on the occasions he has led the side."
Downton added: "Alastair remains an integral part of England cricket and continues to have a vital role in developing our emerging Test side.
"I would like to thank him for his leadership of the one-day side since 2011, a period which saw the team reach number one in the world, Alastair lead the team to more wins than any previous England captain and also make the final of the ICC Champions Trophy."
Cook led England in six of their seven matches in Sri Lanka, making just 119 runs at an average of 19.83.
Morgan made 90 at 12.85. He also led the team in the other fixture, a defeat for which Cook was banned because of an over-rate offence.
Cook's omission was one of three changes to the squad that toured Sri Lanka, with Yorkshire batsman Gary Ballance coming in and seamers James Anderson and Stuart Broad returning from injury.
Durham all-rounder Ben Stokes and Nottinghamshire bowler Harry Gurney were the other players to make way.
England will travel to Australia on January 6 for the tri-series, which also features India. They open their World Cup campaign against Australia in Melbourne on February 14.
England World Cup squad:
Moeen Ali, James Anderson, Gary Ballance, Ian Bell, Ravi Bopara, Stuart Broad, Jos Buttler, Steven Finn, Alex Hales, Chris Jordan, Eoin Morgan (capt), Joe Root, James Taylor, James Tredwell, Chris Woakes.
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Updated Date: Dec 22, 2014 17:07:49 IST