Complex sentence: When she discovers this in January 1999, she decides to keep the child and Conor's daughter Mary (Melanie Clark Pullen) accidentally tells Mark, he is furious and hurt and goes after Conor, beating him up and informing him of the pregnancy.
Split into simpler sentences: When she discovers this in January 1999, she decides to keep the child. When Conor's daughter Mary (Melanie Clark Pullen) accidentally reveals this to Mark, he is furious and hurt and goes after Conor, beating him up and informing him of the pregnancy.