When they hold historians’ attention, French kings’ bastards are studied in a political way, with the aim of understanding the construction, the functioning and even the flaws of monarchy. They are thus examined through their royal – and paternal – filiation. This paper offers to take the other approach, in other words studying royal bastards through their link with maternal kin, from beginning of 17th century to second half of 18th century. Without forgetting the political aspects implied by their peculiar position within royal dynasty, the goal is to question how they can have family relationships, despite the gap between their rank and the illegitimacy of their bounds. More generally, what is at stake is looking at rarely seen familial dynamics, grounded on principles which are at the opposite of conventional noble lineages. To understand them, many approaches can be appealed and tested, such as clientelism, social history or anthropology. To that end, a diversified documentation has been mobilised, notarised documents first, but also royal acts and personal writings from contemporaries.