"Lewis will stay in London and has joined Fulham on loan until the end of the season," Holtby's agent Marcus Noack said.
The move did not go through without acrimony, though.
Noack accused Tottenham of pricing Holtby out of a permanent transfer back to his native Germany.
"Fulham has put much effort into Lewis," he said.
"It is a very well-run club with an excellent manager Rene Meulensteen. The system and philosophy how Fulham plays fits well with Lewis.
"He will have match practice in the second half of the season in his favourite position and then we'll see how things are going by summer.
"A return to the Bundesliga has been shattered due to circumstances we couldn't control."
Holtby joined Tottenham from Schalke 12 months ago for just £1.25million, but the midfielder's camp claimed Spurs wanted £8-10m for the player.
Meanwhile, Mitroglou chose to join Fulham over West Ham - signing from Olympiacos and bolstering the attack after the departure of Dimitar Berbatov to Monaco.
The 25-year-old joins the London club from the Greek champions and has reportedly signed a four-year deal with Rene Meulensteen’s team.
Reports early in the week had indicated that Sam Allardyce had attempted to hijack the deal and lure the Greek international to the Boleyn Ground, but it appears that Mitroglou preferred a move to West London.
Fulham announced the deal on their Twitter page:
Meulensteen captured the Cottagers' third signing of the day, announcing Everton defender Heitinga had joined on a free transfer. The Dutchman has vast experience and helps strengthen a defence weakened by Philippe Senderos's move to Valencia.
And after the deadline had passed, Fulham also announced the signing of Manchester United youngsters Larnell Cole and Ryan Tunnicliffe on permanent deals for undisclosed fees.