The worst-kept secret among those tracking Jeb Bush's presidential campaign is that former president George W. Bush is about to take on a much more prominent role.

Few details of what the 43rd president will do exactly are yet known, but he is expected to campaign with his younger brother at some point in the coming days across South Carolina, where the Bush name remains revered and popular among GOP voters.

Palmetto State voters getting in the car on Wednesday may hear a new radio ad bought and paid for by Jeb Bush's presidential campaign. Aides wouldn't immediately say where and when and on what kinds of radio stations the message will air, but it's expected to be part of a long-planned radio ad campaign targeting primarily conservative talk radio stations.

Former president George W. Bush stars in a new radio ad for his younger brother, Jeb Bush, that begins airing across South Carolina on Wednesday. The former president is expected to campaign for his brother in the Palmetto State in the coming days. (Jeb Bush)

Here's the script:

This is President George W. Bush. We live in troubled times with the military deployed around the world. We need a strong leader with experience, ideas and resolve. There’s no doubt in my mind that Jeb Bush will be a great commander-in-chief for our military. Jeb has dealt with crises as the governor of Florida, and he did so with steadiness, and a calmness necessary in a good leader. He respects the military – he honors their families. He can make the tough decision to keep Americans safe and our country free. And in a time of crisis, he will be a steady hand.

Then Jeb Bush chimes in, saying:

I’m the only candidate for president who’s running on my record – not away from it. And the only candidate with a real plan to defeat ISIS, balance the budget and grow our economy. I’m Jeb Bush, I’m running for president and I approved this message because I’m ready to lead.

The Bush campaign isn't currently airing any television commercials in South Carolina -- they canceled plans for just under $2 million in South Carolina late last year amid a budget crunch. Instead, Right to Rise USA, the super PAC supporting Bush's bid, has said it plans to spend roughly $4.2 million on advertising across the state. PAC leaders haven't specified their plans, but the campaign is likely to mirror what unfolded in Iowa and New Hampshire -- a mix of TV, radio, digital and mail pieces.

Bush is scheduled to make three stops across South Carolina on Wednesday, working his way north from Bluffton, to Mount Pleasant and later Murrells Inlet -- all towns near the coastal population centers of Hilton Head, Charleston and Myrtle Beach. On Thursday, the campaign heads inland, to Florence, Sumter and Columbia.