The 17-year-old midfielder completed a medical in West London yesterday, Monday 28 January, before signing an 18-month contract earlier today. The deal also includes an optional one-year extension.
A teammate of fellow B Team player, Simon Andersson, at Under-17 level, Hammar started his career with IF Bromma of Stockholm, an academy famous for producing some top Swedish talent in recent years.
He was on trial with The Bees earlier in the season when the B squad were beaten 1-0 by Oxford United in July. Six months later, he has signed the paperwork to complete a permanent move to West London.
B Team Assistant Coach Allan Steele said: “Fredrik has been a target for us for a while now, so we are pleased to get him in. In the last transfer window we felt there was just too much competition in midfield. Now with some players out on loan, and some nearing First Team football, we decided the timing was right.
"Fredrik now arrives with men’s football under his belt, a much more experienced player than he was in the summer. He’s a midfielder with a lot of potential who we believe will fit into our style of play well. He will join us when we return from Portugal and I know the boys are keen to see what he can bring to the team.”