PF and DN: When a fellow informs about the change of situation, either being newly entitled to the family allowance, or, on the contrary, no longer, from when should the allowance be given or stopped?

The change would be implemented from the time the allowance is or is no longer eligible according to the documentation. So if the divorce comes into force on 1 September, then that is the month the researcher is no longer eligible for the family allowance. 

In case the family status of a fellow changes during the course of a project, the initial mobility declaration will need to be updated and a new mobility declaration (with the updated family status of the fellow) submitted.
More precisely, in the initial mobility declaration, the end date of the recruitment will need to be modified as follows: the end date will be changed to one day before the fellow acquired a family.
A new mobility declaration will need to be submitted with as a start date, the first day the fellow can be considered as having a family.
In case beneficiaries are confronted with this situation, they should always consult their project officers for further guidance. This change may require an amendment to increase the EU contribution of the project, therefore it is crucial that the project officer is informed.