I genuinely wish him all the best

This may be the most difficult yet the most satisfying and perfect response to anyone who’s asking you about what can you say about your ex. He might have caused you pain and hurt you bad, but your pure and sincere heart still wishes him well in life. Praying for the best for him will not only give you a peace of mind, but also this goes to show how matured you are that despite the pain you’ve been through, your heart remains the same.