In July 2016, Oklahoma toddler, Lincoln Lewis died as the result of a fractured skull. According to the medical examiner’s report, the child’s fatal injuries were caused by “a non-accidental blunt force trauma of the head.” Lincoln’s death was ruled a homicide. His mother’s boyfriend, Dr. Bert Franklin, a 35-year-old married dentist and father of four from Tulsa, was charged with first-degree murder.

TELL DR. PHIL YOUR STORY: Have a story Dr. Phil won't believe?

Lincoln Lewis’ death garnered national media attention soon afterward when prosecutors reported that surveillance video from Roxanne Lewis-Randall’s home showed the moments before and after authorities allege Dr. Franklin fatally wounded the child.

Well before Bert Franklin was accused of killing the 19-month-old, he was Roxanne Lewis-Randall’s boyfriend. She says they began dating about a year prior to Lincoln’s death. Roxanne says when they met, Franklin “was very charming and kind – and just – really nice.” She says “It became serious pretty quick.”

Roxanne claims Franklin told her he was separated from his wife at the time they started dating in June 2015, though they continued to live under the same roof. Roxanne says, “After all this, she (Franklin’s wife) said they never even talked about a divorce.”

Why does Roxanne say she believes her son’s death was the result of Bert Franklin’s jealousy?

In an exclusive interview with Roxanne Lewis-Randall airing Monday, Dr. Phil sits down with the grieving mother to talk about her son, her romance with his alleged killer, and her hopes for her two surviving children.

Bert Franklin says he’s innocent of the charge against him. He vehemently denies hurting Lincoln in any way.

Check here to find out where you can watch Monday’s Dr. Phil.

TELL DR. PHIL YOUR STORY: Have a headline-making story in a small town?

What A Grief-stricken Mom Remembers About Her Toddler’s Sunny Disposition:‘He Was The Happiest’