der Ex
ex
Colloquial short form for a former partner (ex-girlfriend, ex-husband, etc.).
Sie hat neulich zufällig ihren Ex in der Stadt getroffen.
She recently ran into her ex in town by chance.

ex
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ex
Colloquial short form for a former partner (ex-girlfriend, ex-husband, etc.).
Sie hat neulich zufällig ihren Ex in der Stadt getroffen.
She recently ran into her ex in town by chance.

'Der Ex' (the male ex) or 'die Ex' (the female ex) is an informal word used mainly in spoken language and private contexts. In more formal contexts, you would say 'ehemaliger Partner' (former partner) or 'Ex-Mann' (ex-husband).
Sie versteht sich immer noch gut mit ihrem Ex.
She still gets along well with her ex.
The word is a shortened form of nouns that begin with the prefix 'Ex-' (Latin for 'former'), such as 'Ex-Freund' (ex-boyfriend) or 'Ex-Partnerin' (ex-partner, female). This prefix can also be combined with other nouns.
Mein Ex-Chef hat eine neue Firma gegründet.
My ex-boss has founded a new company.
The word adapts to the gender of the person. For a man, you use the article 'der' and say 'der Ex' (the male ex). For a woman, you use 'die' and say 'die Ex' (the female ex).
Gestern hat er seine Ex zufällig auf der Straße getroffen.
Yesterday he ran into his ex on the street by chance.