The move to England has made Llewellyn a potentially leading contender to be a key figure under Tandy after a stop-start international career.
After missing out under Warren Gatland, the centre was given a late call up to the 2025 Six Nations by caretaker boss Matt Sherratt.
He started against Ireland, Scotland and England only for the hamstring injury to deny him a place on the tour to Japan.
Now he aims to provide Tandy with a physical, dominant midfield option at the start of a “new beginning” for the national team.
“I will be judged on my physicality, whether in attack or defence, with the size that I am,” he said.
“It’s how well I can get over the gain line or stop it on the other side of the ball, but I’d like to think I can do a bit more than that.
“We are so expansive at Gloucester and you end up getting a lot of opportunities. That’s really exciting because you know there will be chances, you just have to be one of the players that works hard enough to get on the end of it.”