Duane Vermeulen signed for the Bulls instead of the Stormers because "it was the right thing to do" after the Pretoria-based Super Rugby franchise were "the first team to reach out to me last year".
The two Super Rugby franchises were interested last year in signing the Springboks No.8 for this season, with expectations that he would re-join the Stormers, for whom he played 89 game between 2009 and 2015.
Vermeulen explained his decision on Monday, however, telling Netwerk24: "The Bulls were the first team to reach out to me last year. I felt it was the right thing to do, especially after [then-Western Province Rugby Football Union president] Thelo Wakefield told me that the Stormers would rather invest in their young players.
"I accepted it and moved on.
"The Bulls indicated that I could have a role to play here, and when you get such a chance you have to take it."
Vermeulen left the Stormers in 2015 to join French Top 14 powerhouse Toulon, for whom he played 68 games in the league and European Champions Cup. He joined Kubota Spears in Japan last year, playing seven games in the Top League.
"I missed the team's final two games due to a knee injury, but everything is now sorted," Vermeulen said.
Vermeulen is expected to make his Bulls debut on Sunday, when they play the Stormers as part of the double-header at Cape Town Stadium. The Sharks will play the Lions in the other fixture, with all four teams wearing their Marvel Super Hero jerseys.
And the fact that the Stormers will be wearing 'Thor' jumpers while the Bulls will don 'Captain America' kit has been a source of consternation in the Vermeulen household as the Springboks star is nicknamed Thor.
"I got a hammering on Twitter about that," Vermeulen said laughing at a Bulls media opportunity.
"I don't know exactly how they pick the jerseys, but it is a tough one in the house.. "My two boys are still going on about Thor, but I thought I'd buy them a Captain America jersey. Luckily they got Captain America shields for Christmas, so we have been working on it."