East Grinstead chairman Richard Tramontin said: “We are obviously shocked at this news but I’d like to thank Matt for his efforts since he took over in October 2015. He has put in place a clear philosophy in terms of how he wanted the team to play and the type of player to carry it out, with a structure in place that will hopefully enable us to develop more home-grown first team players in the future.
“We’re disappointed that Matt is not going to be around to continue his hard work but we respect his wishes to develop his own career in management and wish him all the best in his new role.
“We have asked Craig Haylor and Ben Burns, who have worked with Matt as part of his management team, to take charge on an interim basis, starting at Herne Bay on Saturday. In addition, Drew Cooney is going to take on a player-coach role, also with immediate effect.
“We believe they will give us the continuity we need at this time and will be giving them our full support.”
Longhurst moves south to the Pilot Field to replace Steve Watt, who has left Hastings to take the managerial post at Vanarama National League South strugglers Margate.
Longhurst said: “It is with a heavy heart that I have decided to move on to pastures new to progress my own managing and coaching career.
“The club has made big progress over the last fourteen months and there are some fantastic people at the club. The players and staff have been a great credit to themselves and I wish them all the best for the future.
I have ambitions to work as high as I can and to fulfil this I need to continue to learn and progress myself and this is the sole reason for leaving.
“I want to take this opportunity to thank Richard and Brian for giving me the opportunity to manage the club and all the staff and people behind the scenes. A big thank you to the players who have been fantastic and the supporters who have been so welcoming and supportive.
“I will follow Grinstead’s results closely and look forward to visiting the GAC as a supporter at some stage”.