The 21-year-old has now been released from his contract to take up the new playing opportunity outside of Wales.
Director of Rugby Phil Davies said: "We have agreed to let Thomas leave the Blues to pursue other options that he feels will provide him with more regular playing opportunities.
"He is a player that has come through the age grade ranks here at Blues and has been a popular member of the squad who has always worked exceptionally hard and done everything asked of him.
"It has been tough for him in terms of the competition we've got for the number seven shirt with the likes of Sam Warburton, Josh Navidi, Ellis Jenkins and Rory Watts-Jones.
"He now has an opportunity at Gloucester Rugby where he believes he can play more first team rugby. He leaves the region with our very best wishes and thanks for his efforts during his time with the Blues."