diff --git a/api/autoscaling/v2/horizontalpodautoscaler_webhook.go b/api/autoscaling/v2/horizontalpodautoscaler_webhook.go
index 1d7b54d8..588a295f 100644
--- a/api/autoscaling/v2/horizontalpodautoscaler_webhook.go
+++ b/api/autoscaling/v2/horizontalpodautoscaler_webhook.go
@@ -64,6 +64,10 @@ var _ admission.CustomDefaulter = &HPAWebhook{}
 func (h *HPAWebhook) Default(ctx context.Context, obj runtime.Object) error {
 	hpa := obj.(*v2.HorizontalPodAutoscaler)
 	tortoiseName, ok := hpa.GetAnnotations()[annotation.TortoiseNameAnnotation]
+	if !ok {
+		//nolint // We use the deprecated annotation deliberately so that we don't break existing users.
+		tortoiseName, ok = hpa.GetAnnotations()[annotation.DeprecatedTortoiseNameAnnotation]
+	}
 	if !ok {
 		// not managed by tortoise
 		return nil
@@ -126,6 +130,10 @@ func (*HPAWebhook) ValidateUpdate(ctx context.Context, oldObj, newObj runtime.Ob
 func (h *HPAWebhook) ValidateDelete(ctx context.Context, obj runtime.Object) (warnings admission.Warnings, err error) {
 	hpa := obj.(*v2.HorizontalPodAutoscaler)
 	tortoiseName, ok := hpa.GetAnnotations()[annotation.TortoiseNameAnnotation]
+	if !ok {
+		//nolint // We use the deprecated annotation deliberately so that we don't break existing users.
+		tortoiseName, ok = hpa.GetAnnotations()[annotation.DeprecatedTortoiseNameAnnotation]
+	}
 	if !ok {
 		// not managed by tortoise
 		return nil, nil
diff --git a/pkg/annotation/annotation.go b/pkg/annotation/annotation.go
index b4a8b2ee..8a40efd5 100644
--- a/pkg/annotation/annotation.go
+++ b/pkg/annotation/annotation.go
@@ -2,8 +2,11 @@ package annotation
 
 // annotation on HPA and VPA resource.
 const (
+	// Deprecated: TortoiseNameAnnotation - VPA and HPA managed by tortoise have this label.
+	// If an existing HPA has this label, it's automatically replaced with TortoiseNameAnnotation by the controller.
+	DeprecatedTortoiseNameAnnotation = "tortoises.autoscaling.mercari.com/tortoise-name"
 	// TortoiseNameAnnotation - VPA and HPA managed by tortoise have this label.
-	TortoiseNameAnnotation = "tortoises.autoscaling.mercari.com/tortoise-name"
+	TortoiseNameAnnotation = "tortoise.autoscaling.mercari.com/tortoise-name"
 
 	// If this annotation is set to "true", it means that tortoise manages that resource,
 	// and will be removed when the tortoise is deleted.
diff --git a/pkg/hpa/service.go b/pkg/hpa/service.go
index 00ad155d..013f78f8 100644
--- a/pkg/hpa/service.go
+++ b/pkg/hpa/service.go
@@ -668,6 +668,14 @@ func (c *Service) UpdateHPAFromTortoiseRecommendation(ctx context.Context, torto
 		}
 
 		hpa = c.excludeExternalMetric(ctx, hpa)
+		//nolint // We use the deprecated annotation deliberately so that we don't break existing users.
+		if tortoiseName, ok := hpa.Annotations[annotation.DeprecatedTortoiseNameAnnotation]; ok {
+			hpa.Annotations[annotation.TortoiseNameAnnotation] = tortoiseName
+			//nolint // We use the deprecated annotation deliberately so that we don't break existing users.
+			delete(hpa.Annotations, annotation.DeprecatedTortoiseNameAnnotation)
+		}
+		// If HPA has a deprecated annotation, we replace it with a new one.
+		// It allows us to remove a deprecated annotation completely later
 		retHPA = hpa
 		return c.c.Update(ctx, hpa)
 	}