The musician and actor Tomas Forssell [sv]—father of television and radio host Gry Forssell—was his half brother.

[3] He later chose to start acting and applied to the Royal Dramatic Theatre drama school, but failed in the first round of auditions.

[4] He took private acting lessons with director Fred Hjelm [sv] and then he successfully applied to the Teaterhögskolan in Malmö.

[2] In 1981, he had the leading role in the SVT children's television program Christmas calendar titled Stjärnhuset, which won him national recognition.

A year later Brost became a panelist on the ratings success Gäster med gester, which began airing on SVT; he also appeared in several pantomimes.

[10] He also had roles in several films, including Black Jack, Änglagård, Jönssonligan dyker upp igen and The Visitors.