The letter went on to say the leave might be for several weeks but the board was pleased Duncan McQueen had agreed to lead the college in the meantime.
Speaking to the Herald at the time, Conelly confirmed Brooke was on "special leave" for a personal matter but said he could not elaborate on the situation.
The school community was not given any update on the situation regarding Brooke last term, frustrating a number of parents spoken to by the Herald.
McQueen would remain acting principal while the board recruited a new principal. He was formerly principal of the middle college until the role was disestablished during restructuring of the school.
Brooke took on the role of Saint Kentigern College at the start of 2020 when the school decided to merge the Middle College and Senior College into one structure.
Before his appointment at the Pakuranga school, Brooke was principal of ACG Parnell College for three years and principal of Long Bay College before that.
Head of St Kentigern David Hodge also resigned earlier this year because of ill health.
The board also recently advised Independent Schools of New Zealand (ISNZ) that it had appointed Dr Kevin Morris as Executive Trustee, a new role in which he will provide oversight and leadership across the entire organisation, including Saint Kentigern's four schools.
This role replaces and builds on the previous head of Saint Kentigern role and would continue to take the lead in meeting both the educational needs of our students and organisational needs of the trust board, Conelly wrote in the announcement to ISNZ.
In the same letter which announced Brooke's resignation, the board said Morris started in the new role at the start of the month.
Morris is a St Kentigern old boy and has been on the trust board since 2018.
For the past eight years, he has been director of learning and teaching in the office of the vice-chancellor at Auckland University.