The process leading up to and during the defense is roughly as follows:
Assessment Committee: Your supervisor and the chairperson appoint an assessment committee, which must be approved by the PhD school. The PhD school will then inform you that the assessment committee has been approved. The PhD school sends your dissertation to the assessment committee, which then submits a preliminary recommendation back to the PhD school.
Defense: Before the defense, you, your supervisor, and the chairperson of the assessment committee must approve a draft announcement of your defense. Once everyone is satisfied, a notice is sent to everyone at FKF that your defense will take place. The same is announced on social media.
Read more about the defense here: Guide from the NAT PhD School.