Dennis Hastert has made it official that he is going to resign before the end of his term.

Former House Speaker Dennis Hastert will resign his seat in Congress later this year, and not serve out the remainder of his term, FOX News has learned.

The Illinois Republican has informed the House GOP leadership of his early departure, according to Republican sources. No date has been chosen for a formal announcement, which was originally scheduled for Thursday, sources told FOX News, but the resignation is expected to become effective in December or January.

Hastert’s leaving in the middle of the 110th Congress means his Illinois district will have to hold a special election, one more likely to favor a GOP candidate since the party is expected to be more adept at turning out voters in a low-turnout special election.

The 11-term congressman announced on Aug. 17 that he will be stepping down, but did not say whether it would be at the end of the session or before then. He is one of 12 Republican lawmakers to announce their retirements this year.

This will give another Republican or a Democrat the advantage of incumbency in the 2008 election.