West Ham have completed a the signing of
The Wales internationals have been a target of several clubs over the summer with Cardiff desperately needing to slash their wage bill and generate some revenue to allow new boss Dave Jones to buy new players.
Hammers boss Alan Pardew said: "Danny has shown he can compete at the highest level and James is an excellent prospect."
The fee for both Gabbidon and Collins is believed to top £3m, with extra clauses likely for appearances and Premiership survival, while it would be no surprise to see Cardiff take on West Ham in a friendly next year.
Pardew added: "With the signing of James and Danny we now have five of the best young centre backs in the country.
"Danny comes to West Ham United with a lot of experience for a player of his age.
"At just 25 years old he is already a key player for the Welsh national team and has shown a lot of maturity in his performances.
"Pace and agility will be his major assets as Danny makes the transition to the Premier League.
"James is probably lacking experience as he joins the club, but do not underestimate his potential."
While the move leaves a major hole in the heart of the Bluebirds' defence, Jones can now prepare to build his squad for the new season.
Bluebirds owner Sam Hammam said: "Clearly sacrifices have to be made and this is a summer of sacrifices."
Sad to see the lads go, but all the best to them in the Premiership - it can only be a great thing for Welsh football to have yet more players playing in the top flight of English football!