Nick Williams will leave Ulster Rugby at the end of the season and the powerful New Zealander will join fellow Guinness Pro12 club, Cardiff Blues, on a long-term contract from next summer.
Williams - cousin of New Zealand World Cup winner Sonny Bill Williams - joined Ulster in 2012 and was named as the PRO12 Player of the Season at the end of his debut season. He has gone on to make 67 appearances for the Province, scoring 13 tries, during a four-year spell.
Commenting on the move, Williams said: "I've thoroughly enjoyed my time in Belfast. The Ulster people are special and the supporters have always been so good to me. My daughter was born in Ireland so it will always be a special place for our family.
"Rest assured, I'll be giving everything for the team until the end of this season. We have set our targets over the next five months and I want to play my part in us achieving them.”
The 32-year-old back-rower is an explosive ball carrier and has also spent time with Munster and Aironi since moving to Europe in 2008.
Cardiff head coach Danny Wilson said: "Nick has been one of the stand-out performers in the Guinness Pro12 for the last few seasons so we are thrilled that he will join us from next season.
"He is an extremely physical and uncompromising forward who will give us real edge and bring a real winning mentality with him. Nick is undoubtedly a strong ball carrier who is involved in big collisions in both attack and defence.
"We are pleased to bring a player not only of his quality but also with vast experience to the region as we look to enhance our back row options and firepower for the coming seasons."
Williams added: "It is a new challenge for me and I'm excited about what I've heard about what Cardiff Blues are looking to achieve, both on and off the field, in the coming years.
"I feel both physically and mentally as strong as ever and I'm ready to make an impact. Ulster have looked after me so I feel I can really contribute in Wales and in a new environment.
"I spoke to Danny at length about the region and his plans. I'm now looking forward to using my experience to help the team and getting stuck in."
