In general, I’ll be nice and super sweet when attempting to bring the subject and perhaps say something like “please/promise don’t be mad, ok?” A good partner is a forgiving partner for understandable mistakes that will upset them. Don’t forget to be extra grateful and cheerful when they forgive you. Say something like “you’re the best/most understanding” and follow up with a nice back rub (so that they will likely to forgive you again next time lol).
Other than that, decide the best time to bring the subject and judge your loved ones condition. Don’t ask when they’re already upset for other reasons or having too much problem on their plate at the moment. Make them happy, relax, and fill their stomach and then you could ask the possibly upsetting question.