In a sticky spot [m]

This is nothing yo do with my sexual escapades. Its about a boy and a girl who are supposed to get married on 02/14.
The boy say B, dad was a great friend of mine. He was 10 years older to me but we somewhat were close friends. But on 09/2018 he died of a accident. I was very sad then but live moves on. Few days back I came to know B is getting married to a beautiful gal G. B and G had met in college and had fallen in love.
But the irony is G’s mother had at one time (when G was not born) had a secret affair with my friend (B’s Dad).
And she had become pregnant and had delivered a baby gal B.
I was told about this by my friend long back in early 2000’s. Now I am not sure how can i say B n G that they are brother and sisters.
By the way G’s mother had died long back in 2010 types

Source: reddit.com/r/gonewildstories/comments/f1ld2v/in_a_sticky_spot_m