What were the circumstances surrounding Dorian Gray's birth in the book "Picture of Dorian Gray"?

Although Dorian Gray is twenty years old when the story begins, the author describes the circumstances of his birth in Chapter 3.  Dorian is the grandson of the esteemed Lord Kelso, and his mother was the very beautiful Lady Margaret Devereaux.  Margaret married a man of whom her father did not approve, "a penniless young fellow, a mere nobody, a subaltern in a foot regiment, or something of that kind".  Margaret's husband was killed in a duel not long after their marriage, and it was rumored that Lord Kelso himself set the young man up, arranging for "some rascally adventurer, some Belgian brute", to insult his son-in-law in public, and thus necessitating a duel.  The hapless young man was grossly overmatched, and the Belgian "spitted the man as if he had been a pigeon".  Lady Margaret never spoke to her father again, and died within a year, leaving a son, Dorian Gray.  Dorian was raised, ironically, by his grandfather, the man who was so instrumental in making him an orphan (chapter 3).