diff --git a/src/click/core.py b/src/click/core.py
index 6adc65ccd6..4ca8f842bc 100644
--- a/src/click/core.py
+++ b/src/click/core.py
@@ -3145,10 +3145,9 @@ def prompt_for_value(self, ctx: Context) -> t.Any:
                 default = bool(default)
             return confirm(self.prompt, default)
 
-        # If show_default is set to True/False, provide this to `prompt` as well. For
-        # non-bool values of `show_default`, we use `prompt`'s default behavior
+        # Pass show_default to prompt regardless of its type (bool or str).
         prompt_kwargs: t.Any = {}
-        if isinstance(self.show_default, bool):
+        if self.show_default is not None:
             prompt_kwargs["show_default"] = self.show_default
 
         return prompt(
diff --git a/src/click/termui.py b/src/click/termui.py
index 2e98a0771c..fca119dd1c 100644
--- a/src/click/termui.py
+++ b/src/click/termui.py
@@ -60,7 +60,7 @@ def hidden_prompt_func(prompt: str) -> str:
 def _build_prompt(
     text: str,
     suffix: str,
-    show_default: bool = False,
+    show_default: bool | str = False,
     default: t.Any | None = None,
     show_choices: bool = True,
     type: ParamType | None = None,
@@ -69,7 +69,10 @@ def _build_prompt(
     if type is not None and show_choices and isinstance(type, Choice):
         prompt += f" ({', '.join(map(str, type.choices))})"
     if default is not None and show_default:
-        prompt = f"{prompt} [{_format_default(default)}]"
+        if isinstance(show_default, str):
+            prompt = f"{prompt} [{show_default}]"
+        else:
+            prompt = f"{prompt} [{_format_default(default)}]"
     return f"{prompt}{suffix}"
 
 
@@ -88,7 +91,7 @@ def prompt(
     type: ParamType | t.Any | None = None,
     value_proc: t.Callable[[str], t.Any] | None = None,
     prompt_suffix: str = ": ",
-    show_default: bool = True,
+    show_default: bool | str = True,
     err: bool = False,
     show_choices: bool = True,
 ) -> t.Any:
diff --git a/tests/test_options.py b/tests/test_options.py
index f198d10183..c99eb06f02 100644
--- a/tests/test_options.py
+++ b/tests/test_options.py
@@ -1248,6 +1248,20 @@ def test_show_default_string(runner):
     assert "[default: (unlimited)]" in message
 
 
+def test_show_default_string_in_prompt(runner):
+    """When show_default is a string and prompt is enabled, the string is
+    shown in the prompt instead of the actual default value."""
+
+    @click.command()
+    @click.option("--name", default="secret", show_default="custom", prompt=True)
+    def cli(name):
+        click.echo(f"Name: {name}")
+
+    result = runner.invoke(cli, input="\n")
+    assert "Name [custom]: " in result.output
+    assert "secret" not in result.output.split("\n")[0]
+
+
 def test_show_default_with_empty_string(runner):
     """When show_default is True and default is set to an empty string."""
     opt = click.Option(["--limit"], default="", show_default=True)