If a Grand Master joins a unit of Knights, Inner Circle Knights or Demigryph Knights, the unit gains the Immunity (Psychology) special rule for as long as he remains in it.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
If a Grand Master joins a unit of Knights, Inner Circle Knights or Demigryph Knights, the unit gains the Immunity (Psychology) special rule for as long as he remains in it.