I saw this on another forum, and im quite interested to read it:

I think it was a regency novel, although it was possible that their estate was in Scotland. H and h were in a troubled marriage. I think there was a lot of misunderstandings between them which created much angst. This ultimately led to H leaving h perhaps in the belief that she was adulterous. He went to London, possibly overindulging himself whilst there, and jn the meantime h was left abandoned in their remote estate. She was pregnant, which H might only have been made aware of in London, but he dismissed this as another man's claim. She gave birth without much emotional support. He eventually came back to the estate, initially keeping his distance to the child, who was by then toddling around. As h was hurt by his callousness previously, she did not insist that he make his acquaintance with the child. He was slowly warmed over by the child's cuteness and through spending more time with this little boy, had realised that this child could only be his. I think there might be some grovelling on his part after this.
The hero had blue eyes and recognized his son by looking as his eyes around 3ish age.

The op has said the following:
The H knew h was having a baby, and the brith happened early on the book (so no pregrnancy based books or secret baby, more like the paternity is questioned)
H is in london or some major city, doenst leave her for any exotic place.

Not Lord Ruin, Potent Pleasures (not Eloise James), Love Only Once, Paradise Wild,

Sorry for the typos, i've been trying to hunt this book down, and its quite late here.
Any help will be appreciated!