Hi!
I'm looking for a book with: Reunited twins, where they didn't know that they had one and I would like it to be a romance genre (mainly).

I'm looking this "theme" in general, but I have some book in mind.
And I don't know If i made it up or something, but I thing a saw a book were girls (twins - let's name them "A" and "B") find each other, were one of them ("B") is in a happy relationship (boyfriend/husband) and the main character (twin "A") falls in love with her sister's brother/friend of a boyfriend/husband.

Graphic relations:

TWIN A -> sisters/twin to -> TWIN B
...../.......................................\
.../ (falls for).............................\ (married/in relationship with)
MAN A.....-> friend/brother ->.....MAN B


Hope you guys can help me

here's one:
Sisters Found by Joan Johnston (its about reunited triplets)