import re


def replace_last_number(input_string, replace_string):
    """
    Replace the last number with the given replace_string
    :param input_string: str, string to search for the last number
    :param replace_string: str, string to replace the last number with
    :return: str, new string after replacing
    """

    replace_string = str(replace_string)
    regex = re.compile(r'(\d+)(?=(\D+)?$)')
    search = regex.search(input_string)
    if not search:
        return input_string + replace_string

    return input_string[:search.start()] + replace_string + input_string[search.end():]