diff --git a/x-pack/plugins/security_solution/common/endpoint/models/event.ts b/x-pack/plugins/security_solution/common/endpoint/models/event.ts
index 0d6293ad1eb002..fdaef41dbf1180 100644
--- a/x-pack/plugins/security_solution/common/endpoint/models/event.ts
+++ b/x-pack/plugins/security_solution/common/endpoint/models/event.ts
@@ -53,9 +53,9 @@ export function parentEntityId(event: ResolverEvent): string | undefined {
   return event.process.parent?.entity_id;
 }
 
-export function ancestryArray(event: ResolverEvent): string[] {
+export function ancestryArray(event: ResolverEvent): string[] | undefined {
   if (isLegacyEvent(event)) {
-    return [];
+    return undefined;
   }
   return event.process.Ext.ancestry;
 }
diff --git a/x-pack/plugins/security_solution/server/endpoint/routes/resolver/utils/fetch.ts b/x-pack/plugins/security_solution/server/endpoint/routes/resolver/utils/fetch.ts
index fce8e4d9343825..8d7c3d7b731589 100644
--- a/x-pack/plugins/security_solution/server/endpoint/routes/resolver/utils/fetch.ts
+++ b/x-pack/plugins/security_solution/server/endpoint/routes/resolver/utils/fetch.ts
@@ -63,7 +63,7 @@ export class Fetcher {
       await this.doAncestors(
         // limit the ancestors we're looking for to the number of levels
         // the array could be up to length 20 but that could change
-        ancestryArray(originNode.lifecycle[0]).slice(0, limit),
+        Fetcher.getAncestryAsArray(originNode.lifecycle[0]).slice(0, limit),
         limit,
         ancestryInfo
       );
@@ -149,6 +149,20 @@ export class Fetcher {
     return createLifecycle(entityID, results);
   }
 
+  private static getAncestryAsArray(event: ResolverEvent): string[] {
+    const ancestors = ancestryArray(event);
+    if (ancestors) {
+      return ancestors;
+    }
+
+    const parentID = parentEntityId(event);
+    if (parentID) {
+      return [parentID];
+    }
+
+    return [];
+  }
+
   private async doAncestors(
     ancestors: string[],
     levels: number,
@@ -188,7 +202,7 @@ export class Fetcher {
     const levelsLeft = levels - ancestryNodes.size;
     // the results come back in ascending order on timestamp so the first entry in the
     // results should be the further ancestor (most distant grandparent)
-    const next = ancestryArray(results[0]).slice(0, levelsLeft);
+    const next = Fetcher.getAncestryAsArray(results[0]).slice(0, levelsLeft);
     // the ancestry array currently only holds up to 20 values but we can't rely on that so keep recursing
     await this.doAncestors(next, levelsLeft, ancestorInfo);
   }
diff --git a/x-pack/test/api_integration/apis/endpoint/resolver.ts b/x-pack/test/api_integration/apis/endpoint/resolver.ts
index b702914fc16c56..c9356de07f7116 100644
--- a/x-pack/test/api_integration/apis/endpoint/resolver.ts
+++ b/x-pack/test/api_integration/apis/endpoint/resolver.ts
@@ -424,6 +424,7 @@ export default function resolverAPIIntegrationTests({ getService }: FtrProviderC
             )
             .expect(200);
           expect(body.ancestors[0].lifecycle.length).to.eql(2);
+          expect(body.ancestors.length).to.eql(2);
           expect(body.nextAncestor).to.eql(null);
         });