Nathan Hughes has signed a three-year deal with Bristol that will see him leave Wasps at the end of the season.
The Fijian-born England number eight has been an integral part of the Wasps pack since arriving from Auckland in 2013 but has opted to depart the Coventry-based club for the 2019-20 campaign.
"Nathan is a quality rugby player who brings physicality, power and brute strength to our game," Bristol head coach Pat Lam said.
"At 27 years old, we're excited about how much better he can become as we continue to grow as a team.
"We are striving to be a Champions Cup team and a player of Nathan's quality can help us along our journey, on and off the field."
Hughes, who has won all 18 of his England caps under Eddie Jones, is Wasps' most powerful carrier and his departure will leave a big hole at the Ricoh Arena.
"When I talked to Pat about the direction of the club and the ambition at Bristol, it really excited me," Hughes said.
"I've spoken to a lot of guys there and they have been really positive about the environment and the unbelievable support for the Bears in the city.
"There's still a lot I want to achieve and the quality of coaching and the squad at Bristol means that everything is in place to be successful."
In a further blow to Wasps, it has been confirmed that South Africa full-back Willie Le Roux will also be leaving at the end of the season.
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