South Carolina’s disgraced ex-Gov. Mark Sanford is re-entering politics with a run for a soon-to-be-vacant House seat, a strategist with knowledge of his plans said Thursday evening.

“He’s looking all but certain to do it,” a former top aide to the Republican, who did not want to be identified for fear of prematurely revealing the plans, told CNN.

A formal announcement will come soon, the source said.

Sanford will seek the same Charleston-area seat he held in the 1990s. It is being vacated by Rep. Tim Scott, R-S.C., who has just been appointed by Gov. Nikki Haley to replace Sen. Jim DeMint, who suddenly resigned to become head of the Heritage Foundation.

Sanford’s once highly touted political career was derailed in 2009 after his mysterious disappearance -- he had first said he was off “hiking the Appalachian Trail” -- led to an admission of an affair with a woman from Argentina. He served out his second term, but he and his wife divorced, and he is now engaged to his former mistress.

A special election should allow Sanford a rare opportunity for a comeback -- but he could end up facing his ex-wife, Jenny.

Sanford’s first test, the Republican primary, is likely to happen in late March, CNN reports.

Under South Carolina law, the primary must take place 11 weeks after Scott officially resigns, which is expected in early January.

A runoff would take place two weeks after the primary if no candidate receives a majority of votes, followed by a special election in May, which will strongly favor the Republican nominee given the district’s lines.

But Sanford still has to fight to regain his good name. The most recent polls since he left office show that significantly more than half of South Carolina voters view him unfavorably, The Washington Post reports.

Perhaps most intriguing about Sanford’s comeback has been the idea that he could be pitted in the primary against Jenny Sanford, who has said she is considering a campaign of her own. Jenny Sanford distanced herself from her husband soon after the affair went public and was considered a potential Senate appointee before Scott got the nod.

But the strategist said Sanford would not run against his ex-wife, which suggests Jenny Sanford won’t run for the seat.

Other declared or possible candidates, the Post reports, include state Sen. Larry Grooms; state Sen. Tom Davis, who is Sanford’s former chief of staff; Paul Thurmond, the son of the late senator Strom Thurmond and a recently elected state senator whom Scott defeated in a 2010 primary runoff; state House Majority Whip Jimmy Merrill; and state Rep. Peter McCoy.