Mockito: mock both return value with callback method

In mockito, I want to mock a method that returns some value and also has to invoke a callback

For example, here is the service method:

String fetchString(Callback<String> callback);

I want the return value to happen before the callback is invoked. I looked into using Mockito.doAnswer(..) but can't seem to figure out how to make the method invoke the callback after the return statement. Example:

when(mockService.fetchString(any(Callback.class)).thenAnswer(
    new Answer<String>() {
        String answer(InvocationOnMock invocation) {
            ((Callback<String>) invocation.getArguments()[0]).onResult("callback string");
            return "return string";
        }
    });

As you can see in the example above: the callback is invoked before the value is returned. This does't test asynchronous callbacks properly. Is there a way to make the callback method be called after the value is returned?

I know that argumentCaptor can be used here, but is there an alternative that doesn't involve manually calling the callback?

Something that is a combination of doAnswer(..) and thenReturn(..)?