TIFU by accidentally ruining my friend’s proposal surprise

This happened today. And yes, I still feel like an absolute idiot. I have a friend — let’s call him Artem. For the past few months, he’s been planning to propose to his girlfriend. I knew about it because I helped him pick out the ring. He made it very clear: Don’t tell anyone. Especially not her. Today the four of us met up at a café — me, my girlfriend, Artem, and his girlfriend. Just a normal hangout. At some point she starts joking: Everyone around us is getting engaged or married… Mine will probably need five more years to even think about it. We all laugh. And this is where my brain decided to completely betray me. Trying to support my friend, I smiled and said: No, he just wants everything to be perfect. You don’t rush things like that. Silence. She looks at him. He looks at me. I can physically feel my stomach drop. She asks: What things? And instead of smoothly changing the subject like a normal person… I start awkwardly backtracking. Well you kno important things Artem is basically burning a hole through my skull with his eyes. She figured it out. About an hour later she texted my girlfriend: Is he planning something? Did you know? The proposal was supposed to happen next week. Restaurant, photographer, friends hiding nearby — the whole thing. Now she’s pretending she doesn’t know. But she obviously knows. And Artem told me the moment just doesn’t feel the same anymore. I didn’t mean to ruin anything. I was just trying to sound like a supportive friend. Instead, I became the guy who ruined one of the most important moments of his life. TL;DR: Tried to casually support my friend, accidentally hinted at his upcoming proposal, and ruined the surprise.