In social relationships, an ex (plural is exes) is someone with whom a person was once associated. As a prefix, ex- can refer to a variety of different relationships; for example, one might refer to a music group's ex-guitarist, or someone's ex-friend. When used alone, ex as a noun is assumed to refer to a former sexual or romantic partner, especially a former spouse. This often has a derogatory tinge, especially if it refers to unrequited feelings; some French media take advantage of this connotation

Connotation

A connotation is a commonly understood subjective cultural or emotional association that some word or phrase carries, in addition to the word's or phrase's explicit or literal meaning, which is its denotation....

 by calling ex-President of France Valéry Giscard d'Estaing

Valéry Giscard d'Estaing

Valéry Marie René Georges Giscard d'Estaing is a French centre-right politician who was President of the French Republic from 1974 until 1981...

simply the Ex.