FORMER Thornbury Broncos player Billy Vunipola will join his brother Mako at Saracens next season.

Wasps director of rugby Dai Young admitted he was shocked to lose the No. 8, who will leave the club at the end of his contract in the summer after turning down a new deal, but tipped him to have a successful international career.

Billy, 20, joined the Wasps Academy after moving away from Thornbury in 2009 and has been a regular member of the side this season, with his impressive performances earning him a call-up to the England Saxons squad last week.

Prop Mako, 22, has had a slightly different route to the top, coming through the ranks at Bristol before joining Saracens in the summer of 2011 and he committed his future to the Aviva Premiership title contenders by signing a new contract this week.

And Young believes the opportunity to play with Mako was a key reason for Billy opting to move on.

He said: “Billy is a player that the club identified some time ago as one with huge potential and he’s been developed by London Wasps, despite a period when he struggled with illness and injury, into one of the brightest young talents in English rugby.”

“During our contract talks, the player had been adamant that he did not want to leave the club but we know he was under pressure for family reasons to go and join his brother at Saracens. We did everything in our power to keep Billy. “We offered him the contract he asked for. He is playing regularly and he has already got international recognition, so we didn’t see any reason for him to leave. “Although we had heard the whispers about him going to Saracens, we were only officially informed yesterday (Monday) afternoon that Billy was leaving and he had previously signed for them."

“Although we are bitterly disappointed right now, it is only fair for me to say that I believe that Billy will become a top quality international player for years to come and we wish him the best with his career. “There is a long way to go in the season and I am sure he will give his all for Wasps in the coming months.”

Billy is highly regarded by England head coach Stuart Lancaster and will train with the senior squad next week as they prepare for the Six Nations. “I think he is someone who has got tremendous potential,” said Lancaster. “It is a key position, No.8, so I want to make sure he is given the development he needs."