Shotton joined Birmingham on a permanent basis last month after ending last season on loan at St Andrew's from Derby.
Shotton was a regular in his first season at Derby but lost his place following former manager Paul Clement's arrival last summer, making just one start and seven appearances in total.
The former Stoke star then joined Birmingham for a three-month loan stint between January and April, scoring one goal in nine appearances.
Shotton was due to return to pre-season with Derby this summer as he still had a year to run on his contract, but the player has revealed the club's hierarchy wanted him out this summer even though a new manager in Nigel Pearson had just taken over.
"I was disappointed the way things ended at Derby," Shotton told HITC Sport.
"I was informed I wouldn't be in the 18-man squad and I was told I could leave by the owner at the end of season.
"I enjoyed my time at Derby and all the lads at the club are a brilliant bunch, but upstairs in the hierarchy there seemed to be a problem.
"However, I have left that all behind me and I am looking forward to my new challenge at Birmingham and I am raring to go for the start of the new season."
Shotton has joined Birmingham on a three-year deal until the summer of 2019 and Blues boss Gary Rowett had made him one of his top targets as he looks to build a squad capable of challenging for promotion over the coming months.