Formal:
* Je suis désolé, ma chérie. (This is the most literal translation and is suitable for a formal situation.)
Informal:
* Je suis désolé, mon cœur. (This is more affectionate and uses a term for "sweetheart".)
* Pardon, ma chérie. (This is a more casual way to say sorry.)
* Je suis désolée, mon amour. (This is another affectionate way to say sorry.)
* Désolée, mon chou. (This is a very informal and affectionate way to say sorry.)
Tips:
* "Chérie" is a common term of endearment for a girlfriend or wife.
* "Mon cœur" (my heart) and "mon amour" (my love) are more romantic terms of endearment.
* "Mon chou" (my cabbage) is a very affectionate term used between close couples.
Choosing the right phrase depends on your relationship with the person you are speaking to and the situation.