The former Seasider is due to be announced as the Hornets new boss, replacing the departing Roy Hodgson.
It means the 39-year-old will face Blackpool in the Championship next season following Watford’s recent relegation from the Premier League.
Edwards departs Forest Green after guiding the club to League One for the first time in their history in his first season in charge.
Speaking to various news outlets today, Forest Green owner Dale Vince claims Watford only made a formal approach for Edwards earlier today.
“FGR confirms the departure of head coach Rob Edwards,” the club said in a statement.
“Rob was a key part of the team that gained promotion to League One this season.
“We’re disappointed that our support, loyalty and honesty towards Rob has been repaid in this way - with negotiations taking place behind our backs.
“We had no contact from Watford, from whom we might expect less, but in any event this kind of behaviour gives football a bad name.
“We thank Rob for all his work at FGR - forgive him the manner of his departure and wish him well.”
Edwards was assisted at Forest Green by another former Seasider in Richie Kyle, who worked at Bloomfield Road under Gary Bowyer before departing to join the FA.
As for Edwards, he was part of the Blackpool squad that famously won promotion to the Premier League during the 2009/10 season.
Having joined the club in 2008, the former centre-back made 59 appearances during his three years on the Fylde coast.
Edwards also played for the likes of Wolverhampton Wanderers, Barnsley and Fleetwood Town during his 14-year playing career.
Following retirement, Edwards moved into youth coaching with Wolves before having a brief spell as manager of non-league side AFC Telford United.
After returning to Molineux, Edwards also had a spell working with England’s Under-16 and Under-20 sides.
Ex-Blackpool striker Jamille Matt was Forest Green’s top scorer this season, scoring 20 goals in all competitions.
The 32-year-old played for the Seasiders between 2016 and 2018.