adjective former

Hi I would like to ask some questions about the adjective former when followed by such words as president, minister. in this structure former N can appear with the definite article 'the', the indefinite 'a/an' and the zero article:

the former president Clinton was...
former president Clinton was...
jospin, a former PM...

is the use of the articles a question of style 'Timestyle' as it came to be known, especially in headlines? or are there semantic/syntactic constraints ?

thanks for your constributions

The use of any of these articles depends on the context, which you do not give. For example.

We spent the day with Hilary and Bill on their ranch. The former President was in a jovial mood...

Former President Bill Clinton today announced he would back the nomination for the candidate from ....

Jospin, a former MP, is seen here... (one of countless MPs throughout history)

Jospin, the former MP for Chipping Norton under Marsh, said the nude girls in the photographs were artiste models he engaged for his private oils on canvas painting class.