  We discuss the possibilities of testing the recent claims of a relatively
large value of the B --> D' transition form factor through B0--> D' pi+ and B-
--> D' pi- decay modes. To estimate the width of the latter we need the decay
constant of the radially excited D-meson that we computed in lattice QCD with
Nf=2 dynamical flavors and after taking the continuum limit we found
f(D')=117(25) MeV. We also provide an update for the values of the D-meson
decay constants obtained by using maximally twisted mass QCD.
