EXCLUSIVE: The 21-year-old has reached an agreement to join former boss Thomas Tuchel at Signal Iduna Park on a four-year deal once a transfer fee is arranged

By Stefan Doring Mainz star Johannes Geis has reached an agreement to join Borussia Dortmund at the end of the season.The 21-year-old has notched five goals and five assists in all competitions this season despite an inconsistent campaign for Thomas Tuchel's side.Tuchel, who will replace Jurgen Klopp at Signal Iduna Park at the end of the season, is determined to bring the rising midfield star with him, having first signed him from Greuther Furth two years ago.Geis has reached an agreement with BVB over a four-year contract and the two clubs must thrash out a transfer fee, with Mainz eager to recoup between €10 million and €15m for the player.Geis' move is also understood to depend on the future of Julian Baumgartlinger. Mainz remain hopeful that the 27-year-old will sign a new contract with the club but are keen to resolve his future before sanctioning any sales.Schalke, Borussia Monchengladbach and Wolfsburg have also been linked with interest in the Germany Under-21 international.