The Irishman will make his debut for his new team when the Bears clash with the Steelbacks at Edgbaston in the first match of the 2022 Vitality Blast on Thursday night (start 6.30pm).
Stirling played for the Steelbacks in the 2020 Blast competition, lining up twice in the County's two Group stage wins against the Bears.
But this time he will be facing his former team-mates, and he is looking forward to it.
"For the first game it was always written in the stars that it was going to be the case I would be playing against them (the Steelbacks)," said Stirling.
"I have a lot of friends there so I am really looking forward to that game.
"They are a really competitive side, they have a good T20 team and they have been brilliant over the Blast's history.
"We know what they will bring.
"They are a dynamic, hard-hitting team, and they also have a lot of good bowlers, so hopefully we will be ready for them."
The Steelbacks are also going to be ready for what Stirling can bring to the Bears.
The big-hitting Ireland opener was the Steelbacks' top run-scorer as they made the quarter-finals in 2020, and both skipper Josh Cobb and head coach John Sadler will be hoping he has an off-night in Birmingham.
"Paul is a big threat for them," said Cobb.
"We know him but he will know our bowlers as well, so it's about whoever holds their nerve on the day I suppose.
"But we do know plenty about him and fingers crossed we can get him early."
And Sadler added: "Paul is a very good player, and he did pretty well for us when he was here a couple of years ago.
"It is what he does, he goes around the world playing these shorter formats and he is very good at what he does.
"But anybody can have a bad day at the office, and we can just hope he has a bad one against us."