"Because he's not coming from a rugby league club the NRL would have approved his registration immediately which means you can play.
"That's just the rules of the game and we're pretty excited that he's back so it's good for the code.
"He's one of the many superstars of the game. It's good to see him going to the Gold Coast. They're a team that needs a few players to increase their crowds and membership and make them a successful team."
Hayne's signature is a tremendous coup for the Titans after the club embarked on several failed player signings, including Manly playmaker Daly Cherry-Evans' controversial backflip last year on a four-year deal worth $4 million.
Doyle was comfortable the Titans had been able to pay market value for Hayne without breaking the salary cap rules or receiving any special financial assistance from the NRL.
The Titans would have had to satisfy the NRL that their contract offer reflected Hayne's true market value and Doyle was adamant the game's governing body would not authorise his registration if his salary did not reflect his true worth.
"I don't believe that for a minute," he said. "They certainly had some money available in their cap, I don't know how much, but I'm sure this is something they'll be able to justify.
"They could easily fit him in for x number of games this year. If the NRL felt that it was realistic they would approve it and if they didn't then they wouldn't."