Speaking to selected media from the McLaren factory on Tuesday, Brown said: "[Andreas] informed me during the season that he was going to go elsewhere when his contract was up at the end of 2025.
"[It was] probably pretty clear where that destination would be, which was quite understandable, given his background.
"At that time, we intended to continue for the foreseeable future, because the relationship is very, very healthy. And his work discipline is very strong.
"What we were going to do at that point was, at the end of the season, let the world know that that change would come in at the end of the '25 season.
"And, after we intended to go public, the first person I was going to call to see if they would lead McLaren's F1 team is the gentleman sitting next to me, Andrea [Stella] - but not at that point, being sure whether that would be something that he would consider.