Create a model with a foreign key to a table not created by SQLAlchemy

My flask app has a table that I created using mysqlconnector:

import mysql.connector
from .config import host, user, passwd, db_name

connection_pool = mysql.connector.pooling.MySQLConnectionPool(
    pool_size=8,
    host=host,
    user=user,
    password=passwd,
    database=db_name)
connection_object = connection_pool.get_connection()
cursor = connection_object.cursor(buffered=True)

cursor.execute(
            """CREATE TABLE IF NOT EXISTS MyTable (
                ID INT AUTO_INCREMENT PRIMARY KEY,
                name VARCHAR(255) NOT NULL UNIQUE
            )"""
connection_object.commit()

A library that I'm importing (authlib) connects to the same DB using SQL

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

from authlib.integrations.sqla_oauth2 import OAuth2ClientMixin

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+mysqlconnector://user:pwd@host/db'
db = SQLAlchemy (app)

class OAuth2Client(db.Model, OAuth2ClientMixin):
    __tablename__ = 'oauth2_client'

    id = db.Column(db.Integer, primary_key=True)
    smthg_id = db.Column(
        db.Integer, db.ForeignKey('MyTable.id', ondelete='CASCADE'))
    smthg = db.relationship('MyTable')

client = OAuth2Client()
db.session.add (client)
db.session.commit()

During execution, it raises this error:

sqlalchemy.exc.InvalidRequestError: When initializing mapper mapped class OAuth2Client->oauth2_client, expression 'MyTable' failed to locate a name ("name 'MyTable' is not defined"). If this is a class name, consider adding this relationship() to the <class '__main__.OAuth2Client'> class after both dependent classes have been defined.

How can I create a table in SQL Alchemy that contains such a foreign key?