Former Cardiff defender Chris Barker, who had an "outstanding playing career" spanning 17 years and over 500 league games, has died suddenly aged 39.
He was found dead at his home in the city on New Year's Day.
His death is not being treated as suspicious.
Barker made over 150 appearances for Cardiff during a five-year spell after joining from Barnsley in 2002.
The left-back played more than 100 times for Barnsley where he began his league career.
He also had spells at Stoke, Colchester, QPR, Plymouth, Southend and Aldershot.
Barker was lead professional development phase coach at Forest Green.
His former management company World In Motion tweeted: "It is with great sadness that we learn of the untimely and tragic passing at the age of 39 of Chris Barker.
"Chris was a client throughout his outstanding playing career of over 500 League games for clubs including Barnsley, Cardiff City, Queens Park Rangers and Plymouth Argyle.
"Moreover, Chris was a wonderful person, an absolute gentleman and a pleasure to work for."
Barker's ex-teammate, Brighton defender Adam Webster, tweeted: "RIP Chris Barker.
"A former team mate of mine and someone who helped me grow up on and off the pitch @OfficialShots thoughts and prayers go out to his family. RIP barks."
Barker's brother Richard is assistant manager at Rotherham.
A statement released by the League One club said: "Rotherham United were deeply shocked and saddened to learn of the news of the passing of Chris Barker, brother of our assistant manager Richard.
"We offer our deepest condolences to the family and friends of the Barker family whilst reaffirming that the thoughts of everyone at the football club, and indeed the town, are with Richard at this incredibly difficult time."
A South Wales Police statement read: "Police can confirm the sudden death of a 39 year-old man who was discovered at his home address in the Cyncoed area of Cardiff at approximately 2pm on New Year's Day.
"His death is not being treated as suspicious and the Coroner has been informed."