How to make a child entity automaticially reference back to parent entity when created using inline entity form? Here is the example:

'Parent' Content Type = Author


field1: Name
field2: Age
field3: Picture
field4: Entity Reference to Books (inline entity form widget)


'Child' Content Type = Books


field1: Title
field2: Description
field3: Entity Reference to Author using prepopulate (need help)


Author has entity reference to Books using Inline Entity Form. So when creating an "Author", we can add "Books" they have written inline.

When a user visits an individual "Book" page, I want a field that links back to the "Author" who wrote it. How can I create this link automatically when creating a "Book" inline?

I assume I have to create a Book field3 that is an Entity Reference to Author that uses prepopulate. But I have not been able to configure this correctly to get it working as wanted. Any ideas?
This has been acheived using Rules:

Export of Rule:

{
        "rules_ifs_backlink_populator" : {
        "LABEL" : "IFS backlink populator",
        "PLUGIN" : "reaction rule",
        "ACTIVE" : false,
        "REQUIRES" : [ "rules" ],
        "ON" : [ "node_insert", "node_update" ],
        "IF" : [
          { "node_is_of_type" : {
              "node" : [ "node" ],
              "type" : { "value" : {
                  "auction" : "auction",
                  "estate_sale" : "estate_sale",
                  "garage_sale" : "garage_sale"
                }
              }
            }
          }
        ],
        "DO" : [
          { "LOOP" : {
              "USING" : { "list" : [ "node:field-ifs-add" ] },
              "ITEM" : { "list_item" : "Current list item" },
              "DO" : [
                { "component_rules_create_entity_reference_back_link_" : { "child_param" : [ "list-item" ], "parent_param" : [ "node" ] } }
              ]
            }
          }
        ]
      }
    }


Export of Component:

{ "rules_create_entity_reference_back_link_" : {
    "LABEL" : "create entity reference back link ",
    "PLUGIN" : "rule",
    "REQUIRES" : [ "rules" ],
    "USES VARIABLES" : {
      "child_param" : { "label" : "Child Parameter", "type" : "node" },
      "parent_param" : { "label" : "Parent Parameter", "type" : "node" }
    },
    "IF" : [
      { "AND" : [
          { "node_is_of_type" : { "node" : [ "child-param" ], "type" : { "value" : { "ifs" : "ifs" } } } },
          { "entity_has_field" : { "entity" : [ "child-param" ], "field" : "field_auction_ref" } },
          { "data_is_empty" : { "data" : [ "child-param:field-auction-ref" ] } }
        ]
      }
    ],
    "DO" : [
      { "data_set" : {
          "data" : [ "child-param:field-auction-ref" ],
          "value" : [ "parent-param" ]
        }
      }
    ]
  }
}