It's a huge spoiler,
Yes, the prince is the ml, not walter, they only have 3 years of age gaps. Walter (Leticia's friend) is actually some kind of jerk.
Actually, the romance is really slow because the story really REALLY focuses on cases and the villains (yes, plural). There's no marriage between Leticia and the prince, but they started dating.
I bought the novel from Malaysia, even though I'm not malay. I just joined the tele, and I chatted with the owner.

Do not tell me the male lead is the prince. I can't do this. he looks so much older than her, I had a gf the same age as me when I was 13 until I was 15, and I couldnt even conceive of being attracted to a 10/12 yr old