DETROIT — Michigan's Republican governor announced Friday that Democrat John Conyers' congressional seat will not be filled until the regularly scheduled November election, leaving it vacant for nearly a year.

Gov. Rick Snyder decided the post will be listed twice on the August primary and November general election ballots. While unlikely, it is possible voters could choose one candidate to fill the vacancy until January 2019 and elect another to a full two-year term after that.

It is unusual for a congressional district to stay vacant for so long, according to a review of roughly 100 vacancies and successors listed on the House website for the last 20 years. The longest time a seat stayed empty was about 10 months — both in 2014, when Rep. Melvin Watt of North Carolina left to head the Federal Housing Finance Agency, and 2006, when Rep. Bob Menendez of New Jersey was appointed to the Senate.

Snyder said he opted against having an earlier special election to give potential candidates ample time to decide about running, provide voters in the predominantly Democratic district more options and save money.

Related: John Conyers retires from Congress, endorses son, amid harassment scandal

The 88-year-old Conyers, who was facing a House Ethics Committee investigation over claims by former staffers, cited health reasons for his resignation Tuesday.

Snyder's office said it consulted with Wayne County leaders before making a decision. The 13th Congressional District Democratic Party Organization backed the decision, too.

"In order to allow several months for that to take place and to reduce the financial burden on local taxpayers, the primary and general elections will be held when regularly scheduled elections are already occurring," Snyder said in a statement.

The filing deadline is April 24 for both elections. Whoever wins the special election will serve next November and December, and — if he or she also wins the regular race — will serve a two-year term starting in 2019. A Snyder spokeswoman said it could have cost up to $2 million if the special elections were scheduled on non-regular election dates.

Detroit, a city of about 680,000, currently does not have any resident serving in Congress.

Former Michigan Department Party Chairman Mark Brewer tweeted that Snyder "continues to give the back of his hand to urban areas whether it's emergency managers, poisoned water, and now being denied representation in Congress for nearly a year."

John Conyers retired amid allegations by about a half-dozen women who once worked for him that they were harassed and touched inappropriately. He has denied the allegations. Conyers first was elected in 1964.

Related: John Conyers III arrested but not prosecuted in domestic abuse case

Some colleagues in the House had urged Conyers to resign. When he did, he endorsed his 27-year-old son, John Conyers III, to succeed him. The younger Conyers, a partner with a Detroit-based, minority-run hedge fund, posted on Twitter this week that he has not decided whether he wants to run for his father's old seat. He has since deleted his Twitter account. The Associated Press has been unable to reach him for comment.

Democratic state Sen. Ian Conyers, John Conyers' grand-nephew, has said he will run.

Fellow Democratic state Sent. Coleman Young II is expected on Monday to announce his candidacy, his spokesman said.

Conyers III never has been elected to a public post. Ian Conyers won a special election in 2016 for his seat. Young was elected in 2010 to the Michigan Senate. He served in the state House from 2005 to 2010.