Clodagh McKenna appeared on the show on Tuesday to demonstrate to viewers how to bake an elderflower and lemon drizzle cake.
But it is when Holly chimes in expressing how much Clodagh loves the cake that she makes the embarrassing slip-up.
“This [cake] is so good and you love it so much that you had it in your wedding cake,” Holly said.
Visibly shocked by Holly revealing her secret live on TV, Clodagh replies: “It’s going to be in my wedding cake in August but I wasn’t going to tell anybody.”
“Oh!” Holly exclaims as the camera pans to her with her hand covering her mouth, realising her blunder.
Philip also hung his head in dismay at his co-host’s faux pas.
“Don’t be silly, it’s not that big a deal, I want to give you a hug but I can’t,” Clodagh said.
Holly replied: “You said it to me earlier … oh my god I’m so sorry.”
The presenter clearly still reeling from her mistake as she scrunched up her nose.
“Don’t be so silly, oh my god don’t be so silly,” the Irish chef responded, reassuring Holly.
The crew found the whole situation hilarious and could be heard laughing in the background.
Meanwhile, Phillip attempts to diffuse the awkwardness by sipping on his elderflower cocktail.
“Oh god, what has happened,” he said, before taking another gulp.
Phillip then jokes: “Is that a break? I can feel a break in the distance.”
“I’m so sorry,” Holly apologies once more.
Though Holly wasn’t the only one to make a gaffe in this segment.
Earlier on in the show, when the three were making elderflower cocktails, Clodagh also suffered from a slip of the tongue.
“Oh sh*t!” she says as she attempts to shake the cocktails, leaving Holly and Phillip lost for words.
Clodagh apologies as the two co-hosts laugh and Phillip remarks: “She does tend to forget she’s actually on the telly.”
You can certainly count on the unexpected to happen when watching This Morning.