According to his biographer William Manchester, Winston was most likely conceived before the marriage, rather than born prematurely. A recent biography has stated that he was born two months prematurely after Lady Randolph "had a fall."[13] When asked about the circumstances of his birth, Winston Churchill would reply, "Although present on the occasion, I have no clear recollection of the events leading up to it."[12] Lady Randolph's sisters believed that the biological father of the second son, John (1880–1947) was Evelyn Boscawen, 7th Viscount Falmouth.[14]

Lady Randolph is believed to have had numerous lovers during her marriage, including Karl Kinsky, the Prince of Wales (the future King Edward VII), and Herbert von Bismarck.[15]

She was rumored to have had over 200 partners

http://www.dailymail.co.uk/news/article-1083772/Earls-counts-future-King--200-lovers-younger-son-As-new-documentary-reveals-wonder-high-society-wits-called-Winston-Churchills-wayward-mother-Lady-Randy.html

Throughout his childhood he constantly wrote his his mom letters and asked her to visit him at school. She would barely return his letters and only visited him a couple of times. She was literally too busy planning parties and banging random dudes.

Later in Churchill’s life, some of the dudes she had sex with helped his career

(http://www.autoadmit.com/thread.php?thread_id=3861990&forum_id=2#35171641)