diff --git a/reference-artifacts/Custom-Scripts/lza-upgrade/src/config/global-config.ts b/reference-artifacts/Custom-Scripts/lza-upgrade/src/config/global-config.ts
index 7eb9dc900..3be9cb078 100644
--- a/reference-artifacts/Custom-Scripts/lza-upgrade/src/config/global-config.ts
+++ b/reference-artifacts/Custom-Scripts/lza-upgrade/src/config/global-config.ts
@@ -2237,6 +2237,7 @@ export class GlobalConfig implements t.TypeOf<typeof GlobalConfigTypes.globalCon
     const aseaStacks: t.AseaStackInfo[] = [];
     for (const account of mappingJson) {
       this.externalLandingZoneResources?.accountsDeployedExternally.push(account.accountId);
+      let nestedStackPhysicalIds: string[] = [];
       for (const stack of account.stacksAndResourceMapList) {
         const phaseIdentifierIndex = stack.stackName.indexOf('Phase') + 5;
         let phase = stack.stackName[phaseIdentifierIndex];
@@ -2249,6 +2250,11 @@ export class GlobalConfig implements t.TypeOf<typeof GlobalConfigTypes.globalCon
         // Delete outputs from template. IMPORT_ASEA_RESOURCES stage will write required information into SSM Parameter Store.
         // delete stack.template.Outputs;
         await fs.promises.writeFile(templatePath, JSON.stringify(stack.template, null, 2));
+        for (const cfnResource of stack.resourceMap) {
+          if (cfnResource.resourceType == 'AWS::CloudFormation::Stack') {
+            nestedStackPhysicalIds.push(cfnResource.physicalResourceId);
+          }
+        }
         aseaStacks.push({
           accountId: account.accountId,
           accountKey: account.accountKey,
@@ -2257,14 +2263,15 @@ export class GlobalConfig implements t.TypeOf<typeof GlobalConfigTypes.globalCon
           resources: stack.resourceMap as t.CfnResourceType[],
           templatePath,
           phase,
-          /**
-           * ASEA creates Nested stacks only for Phase1 and Phase2 and "stack.stackName.substring(phaseIdentifierIndex)" doesn't include accountName in it.
-           * It is safe to use string include to check if stack is nestedStack or not.
-           * Other option is to check for resource type in "Resources.physicalResourceId" using stackName
-           */
-          nestedStack: stack.stackName.substring(phaseIdentifierIndex).includes('NestedStack'),
+          nestedStack: stack.parentStack ? true : false,
         });
       }
+      for (const physicalId of nestedStackPhysicalIds) {
+        const nestedStack = aseaStacks.findIndex((stack) => physicalId.includes(`:stack/${stack.stackName}/`));
+        if (nestedStack > -1) {
+          aseaStacks[nestedStack].nestedStack = true;
+        }
+      }
     }
     return aseaStacks;
   }
diff --git a/reference-artifacts/Custom-Scripts/lza-upgrade/src/resource-mapping.ts b/reference-artifacts/Custom-Scripts/lza-upgrade/src/resource-mapping.ts
index 6d9b13188..42c4768cc 100644
--- a/reference-artifacts/Custom-Scripts/lza-upgrade/src/resource-mapping.ts
+++ b/reference-artifacts/Custom-Scripts/lza-upgrade/src/resource-mapping.ts
@@ -268,19 +268,26 @@ export class ResourceMapping {
       (stackAndResource): stackAndResource is Promise<StacksAndResourceMap> => stackAndResource !== undefined,
     );
     const stackAndResourcesList = await Promise.all(validStackAndResourcePromises);
+
+    const allNestedStacksPhysicalIds: string[] = stackAndResourcesList.flatMap((stack) =>
+      stack.resourceMap
+        .filter((resource) => resource.resourceType == 'AWS::CloudFormation::Stack')
+        .map((resource) => resource.physicalResourceId),
+    );
+
     const allNestedStacks = stackAndResourcesList.filter((stackAndResource) =>
-      stackAndResource.stackName.includes('NestedStack'),
+      allNestedStacksPhysicalIds.find((physicalId) => physicalId.includes(`:stack/${stackAndResource.stackName}/`)),
     );
+
+    const allNestedStackNames = allNestedStacks.map((stackAndResource) => stackAndResource.stackName);
+
     stackAndResourcesList.forEach((stackAndResource) => {
       const nestedStacks = this.getNestedStacks(stackAndResource, allNestedStacks);
       if (nestedStacks) {
         stackAndResource.nestedStacks = nestedStacks;
       }
-      const parentStack = this.getParentStack(stackAndResource);
-      if (parentStack) {
-        stackAndResource.parentStack = parentStack;
-      }
-      if (!stackAndResource.stackName.includes('NestedStack')) {
+
+      if (!allNestedStackNames.includes(stackAndResource.stackName)) {
         stackAndResourceMap.set(
           `${stackAndResource.environment.accountId}-${stackAndResource.environment.region}-${stackAndResource.stackName}`,
           stackAndResource,
@@ -291,14 +298,6 @@ export class ResourceMapping {
     return stackAndResourceMap;
   }
 
-  getParentStack(stackAndResource: StacksAndResourceMap) {
-    if (stackAndResource.stackName.includes('NestedStack')) {
-      const stackNameArr = stackAndResource.stackName.split('-');
-      return `${stackAndResource.environment.accountId}|${stackAndResource.environment.region}|${stackNameArr[0]}-${stackNameArr[1]}-${stackNameArr[2]}`;
-    }
-    return undefined;
-  }
-
   getNestedStacks(stackAndResource: StacksAndResourceMap, nestedStacks: StacksAndResourceMap[]) {
     const phaseIndex = stackAndResource.stackName.toLowerCase().indexOf('phase');
     // checks the length of the stack to determine if it is the nested stack or parent stack