The actor recalled his "The Bodyguard" costar's 2012 funeral during an appearance on Dax Shepard's "Armchair Expert" podcast, revealing an unfortunate moment he had while preparing for his friend's farewell.

Costner, who was one of 8 people to speak at the singer's funeral, was asked ahead of the ceremony to shorten his speech ... so CNN and other networks could air commercials during the broadcast.

Kevin said the convo went like this ... "Somebody said, ‘CNN’s here, they wouldn’t mind if your remarks were kept shorter because they’re going to have commercials.’ And I said, 'They can get over that. They can play the commercial while I’m talking, I don’t care.'"

Ya gotta love his commitment ...  he said he'd carefully crafted his 17-minute speech -- something he was hesitant to undertake, but did so when Dionne Warwick asked -- and he wasn't about to make last-minute edits.

KC continued ... "[I] went back to that church in Newark and it was filled. It was electric. There were two bands playing, the church was alive. It was like, boom!"

Costner and Houston got close while filming their 1992 romance thriller, in which he plays a bodyguard hired to protect her character from a stalker. The film and its soundtrack -- including "I Will Always Love You" -- became mega hits.

Costner remembered Whitney recording the Dolly Parton classic, saying ... "She sang the first part of it a cappella and musically the world was never the same. We have a moment of her in that movie we’ll never ever forget that and I think that when movies are working at their best, that’s what can happen."