Caught out by the question, Curtis revealed his Love Island co-star’s secret, which she’d been hiding from family members.
He spluttered: “She’s gone to Ireland, I believe. I can’t say what for, because it’s a surprise.
“It’s her brother’s birthday and there’s a surprise party. There, I’ve said it. I hope he isn’t watching!”
Curtis’ slip up comes after he announced he’d landed two huge new jobs, weeks after leaving the hit ITV2 show.
After putting on two stone during his time in the Spanish villa, he has been unveiled as the new face of Weight Watchers.
A source told The Sun: “Curtis is delighted with the deal and can’t wait to get started on the healthy recipes.
“He wants to feel confident in his swimwear again and get a six-pack again like his brother AJ. He’d hate to be known as the bigger brother.”
Additionally, Curtis is joining the team of Hits Radio Breakfast, being enlisted as the show’s official Strictly Come Dancing correspondent.
Accepting the position on Thursday’s show, hosted by Fleur East, Greg Burns and James Barr, Curtis said: “I would love to! Dancing is my background. Strictly, I love it.
“I’ve been on Dancing with the Stars in Ireland. I’ll give you all the best inside gossip, I know somebody who’s in the business!”
Adding about why it is such a dream role for him, Curtis joked: “I get to talk about AJ in a bad light!”