Saints coach Ross Lyon caused shockwaves through the club late yesterday when he announced he was leaving to coach Fremantle.

It had been widely believed Lyon would accept a new four-year deal with the club, and the news was to be announced yesterday.

Instead, the coach informed St Kilda of his decision and cut short the meeting with no explanation as to why he was moving.

St Kilda have refrained from making any criticism over his shock decision, and maintain he will always be welcome at the club.

The move means the club now join three other AFL clubs on the hunt for a senior coach.  

Assistant coach Robert Harvey will be the club's interim coach.