Speaking of the signing, Cardiff Blues Director of Rugby, Phil Davies, said: "I am really pleased to have re-signed Gethin. We started the year knowing we had a young squad and it has been a massive season of progression, sometimes the results have not gone our way.
"Gethin will be coming back to an environment that is a little different from the one he left and I think, hopefully, he will enjoy it and I know that he will add a massive amount to the group."
Cardiff Blues CEO, Richard Holland, added: "Gethin is undoubtedly a quality player having played for Wales for a decade and toured with the Lions twice. A lot of hard work has gone on behind the scenes to bring Gethin back to Wales and we are delighted that he has signed with the Cardiff Blues."