diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index 601cad1f1a..3466b47cd3 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -2519,6 +2519,13 @@ system and gives an overview of their function and contents.
       external tools. See the :ref:`ref-classes-kernel-yocto` class in
       ``meta/classes-recipe`` to see how the variable is used.
 
+   :term:`EXTERNAL_KERNEL_DEVICETREE`
+      When inheriting :ref:`ref-classes-kernel-fitimage` and a
+      :term:`PREFERRED_PROVIDER` for ``virtual/dtb`` set to ``devicetree``, the
+      variable :term:`EXTERNAL_KERNEL_DEVICETREE` can be used to specify a
+      directory containing one or more compiled device tree or device tree
+      overlays to use.
+
    :term:`KERNEL_LOCALVERSION`
       This variable allows to append a string to the version
       of the kernel image. This corresponds to the ``CONFIG_LOCALVERSION``