Richie Kyle will join new Watford manager Rob Edwards at Vicarage Road.
The pair worked together in their successful season at the New Lawn, where they took Rovers from League Two to League One at the first time of asking.
Kyle previously had worked as an assistant coach with the Canadian women's national team, as well as previously holding coaching positions at both the FA and Blackpool FC.
He joined Forest Green at the same time as Edwards and the duo will continue their working relationship at Vicarage Road from the end of this season.
Edwards was named as the Hornets' new boss yesterday afternoon after discussions were held with both him and ex-Watford captain John Eustace.
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