The back-rower turned in a man-of-the-match performance in the 34-23 win over Newport Gwent Dragons on Friday to cement the West Walians’ place in the inaugural European Rugby Champions Cup next season.
But he will leave his home region at the end of the season and head for the capital, linking up with this weekend’s opponents as he bids to add to his tally of a handful of Wales caps.
“I am sure it will be emotional,” said Turnbull, ahead of his goodbye to the region where he has spent eight years.
“I said a few weeks ago I was fully committed to the Scarlets, I owe it to them. I have been here eight seasons now and want to finish with a bang, everyone around here does.
“Even though I am moving on, I am still going to support the Scarlets, I am still going to be a fan – I have been since I was a young boy.
“I am going to miss this place, but it is going to be a new challenge. I am going in to the Blues to try to set my stall out early doors and hopefully I will get some game time in my favourite position of six.”
Saturday will also be the last time Lions centre and Turnbull’s former academy team-mate Jonathan Davies pulls on the Scarlets jersey as he prepares for his move to French giants Clermont Auvergne.
Davies’ exit will also add to the sense of occasion for Turnbull, although he insists that it isn’t the end of an era for the Scarlets and he is tipping the talent to keep coming through the ranks in Llanelli.
“The guys here are friends and a lot of boys have grown up together. Myself and Jon came into the academy at the same time. There were five of us that year and we are the last two and both leaving at the same time, which is a bit sad,” added Turnbull.
“But the Scarlets are renowned for their development of young players and there is a whole host of players coming through to fill those gaps. I am sure the Scarlets will only go upwards from here.”
