Kenny Gamble and Leon Huff are "honored" to have written and produced "TSOP (The Sound of Philadelphia)" -- aka the theme to "Soul Train," which has been playing throughout the world in the wake of host Don Cornelius' death on Wednesday.

But Gamble recalls that he had to talk Conelius into having a theme song at all.

"I was really happy for Don when he moved to California and ('Soul Train') got so big," Gamble tells Billboard.com. "I used to talk to him a couple times a week, and I said, 'Don, you've got to get a theme song. Johnny Carson's got a theme song. Bob Hope's got 'Thanks For the Memories.' For a while he was like, 'Nah...,' but finally he was like, 'All right, all right, you sold me,' so I said, 'Come on to Philly. Let's see if we can get one."

Photos: Don Cornelius Through The Years | Celebs Mourn on Twitter

Cornelius came to Philadelphia in early 1974 for a weekend writing session that Gamble acknowledges did not go well at first. "Huff and Thom Bell and myself had been working on some different concepts," Gamble remembers. "They were OK, but it just didn't hit us. Don said, 'Hey man, I'm going back to California. I've got to tape the show,' but I said, 'Don, wait one more day. Let's go back into the studio.' So we took Don back to hotel, and Huff and I came back to the office and tinkled on the piano and messed around with a lot of different ideas. Once we came up with that simple thing, 'Soul train, soul train, dah dah dah dah DAH dah...,' everything fell into place."

Gamble and Huff recorded "TSOP" with MFSB, the Philadelphia International Records house band, and the Three Degrees singing the vocal parts. The song hit No. 1 on the Billboard Hot 100 and on the Hot Soul Singles chart in April of 1974, and on the Easy Listening Singles survey in May. And Cornelius, according to Huff, regretted that he didn't let the duo use "Soul Train" in the tune's official title.

"He was like, 'I don't want anybody else to have my brand but me,' " Gamble says. "We said, 'But that's YOUR theme song.' He said, 'Nah. Call it anything you want. Don't call it the 'Soul Train' theme. So we called it 'TSOP' and it became a No. 1 record, and every time we'd see him after that he'd say, 'Dumbest move I ever made.' But it's OK. It locks us in with each other forever."

Gamble says he and Huff were shocked by the news of Cornelius' death on Wednesday but said they had nothing but fond memories.

"He was a wonderful man," says Gamble, who last saw Cornelius during a visit to Los Angeles from the Grammy Awards in 2010. "He had a great vision that's part of the American culture forever. People all over this planet know about 'Soul Train,' and they know it came from America. 'Soul Train' provided an opportunity for Gamble & Huff and Motown and Stax and all the black artists who could not get a break. He left a great legacy."