CHARLESTON, S.C.—A recount has confirmed that former South Carolina Gov. Mark Sanford will face ex-Charleston County Councilman Curtis Bostic in a Republican runoff for a congressional seat.

Bostic finished ahead of state Sen. Larry Grooms on Tuesday, but the unofficial margin was so close a recount was needed. The final numbers showed Bostic defeated Grooms by 524 votes.

The winner of the April 2 runoff faces Democrat Elizabeth Colbert Bush in a special election May 7. She is the sister of comedian Stephen Colbert.

The seat was left vacant when Gov. Nikki Haley last year appointed Tim Scott to a U.S. Senate seat left vacant by the resignation of Jim. DeMint.

Sanford is waging a political comeback after his career was sidelined by his revelation of an extramarital affair.