Lewis Dobbin is set to work under a new manager during his spell at Derby County.
The Everton forward joined the Rams on a season-long loan in August to enhance his encouraging progress.
Dobbin, 19, made three Toffees appearances last season and signed a new contract at Goodison Park until the summer of 2025.
But after spending pre-season with Frank Lampard’s side, the Everton boss was keen to expose the youngster to regular senior football this term.
He moved to Derby while Liam Rosenior, who succeeded Wayne Rooney in the hot seat after the club’s relegation from the Championship, was interim manager.
Warne was prised from Rotherham United and has been tasked with leading the Rams back to the second tier.
He guided Rotherham to three promotions from League One and leaves with the club sitting a highly-commendable eighth in the Championship.
A statement on Derby’s website said: “As was made clear in the summer, the board intended to take a period of time evaluating every aspect of the club and having done that, we believe Paul’s track record of success at this level fits perfectly into our long-term strategy.
“He has won promotion three times from League One in almost 300 matches as a manager, as well as the Papa John’s Trophy last season, and his recent achievements with Rotherham United highlight his ability and experience, two factors which will be vital in this pivotal season for Derby County.”
Derby were the favourites to be promoted from League One but currently sit seventh.
Dobbin has made 10 appearances so far and awaits his maiden senior goal.