By Brian Mansfield, Special for USA TODAY

Elvis and Martina McBride spend a Blue Christmas together.

Martina McBride was just shy of 2 when Elvis Presley filmed his 1968 "comeback" TV special. This year, the country singer steps back in time 40 years to join the King of Rock 'n' Roll in a video for Blue Christmas.

The effect is similar to Celine Dion's American Idol duet with Presley on If I Can Dream in 2007, but producer George Flanigen says the process used for the illusion was entirely different.

"They took Elvis out of the '68 special and put him on the Idol stage," he says. "We were taking Martina to the '68 special."

The posthumous collaboration also appears on Elvis Presley Christmas Duets, a new album that pairs Presley with singers such as Carrie Underwood, Amy Grant and Olivia Newton-John.

In the original footage — the only existing video of Elvis performing a Christmas song — a leather-clad Presley appears with his band on a small stage at the center of a studio audience. In the video, McBride walks out of the audience and sits next to him.

"There's a spot between (guitarist) Scotty Moore and Elvis that's open, like somebody should have been sitting there," says Flanigen. "We're like, 'We could probably figure a way to put her with Elvis.'

"We scoured the footage and picked shots of Elvis throughout the whole special to be able to put them together. There are shots where he and Martina share the frame, where he looks over at her, where she looks back at him and sings and smiles."

McBride filmed her parts in front of a green screen. "It took four weeks" to piece together, Flanigen says.