1:12PM BST 12 Aug 2011
The 29-year-old left the Britannia Stadium in January after a less-than-satisfactory 18 months, expressing his desire to play in the Bundesliga.
However, he has secured a swift return to England to join Owen Coyle's side.
"I had good talks with the manager and we spoke a lot about football and his ambitions for the club and I wanted to be part of that," said the former Middlesbrough player.
Bolton manager Coyle was pleased to have brought some variety and experience into his side.
"We are delighted to have secured the loan for Tuncay," he said.