London Wasps fly-half Nicky Robinson will leave the club at the end of the season after agreeing to join Bristol, according to reports.
Robinson joined Wasps in 2011 and has battled this season for a starting spot with fellow Welsh fly-half Stephen Jones.
The move is seen as another major signing for championship club Bristol after already agreeing terms with other Premiership players including Peter Buxton, Mark Sorenson, Andy Short and Errie Claassens.
"Nicky is a significant signing for us," said Middleton to The Post.
"He had a fair bit of Premiership interest - a lot of Premiership offers - and I'm over the moon that he chose us.
"I sat with him a couple of weeks ago and really had a good chat with him about what we're doing and he really bought into it, so I'm chuffed.
"He'll bring us a lot of leadership, a lot of experience, and he's a guy who plays at 10 in a way that suits the Bristol fashion style of rugby."
"He's highly rated everywhere he's been - Cardiff Blues rated him highly, Gloucester rated him highly and he did very well for them.
"If you look at his statistics in the Premiership for Gloucester, he was very good there. I'm hugely excited, particularly by the fact that a guy who had so much interest from elsewhere decided to buy into what we're doing here."