Kristen Stewart and Robert Pattinson had been planning to have a baby together before she was caught cheating on him.
The 22-year-old actress and the 26-year-old actor - who have been together for four years - had reportedly been talking about starting a family before she wrecked their plans by having a fling with her married Snow White and the Huntsman director Rupert Sanders.
A source close to the pair - who met on the set of the first Twilight Saga movie - said: "They had been talking about having a baby together once Twilight ended, which is what makes this so extra-painful. Kristen knew how badly Rob wanted to start a family, and it was a subject that had dominated their conversations in recent months.
"Rob would be a great father, and having a baby would probably have brought them even closer together."
Although Stewart and Pattinson have not released a statement on the future of their relationship, Stewart fears there is no way back for them and their baby dreams are over.
The source continued to the National Enquirer magazine: "Kristen fears she'll never have the chance to get Rob back, and that their baby dreams are now totally shattered. Kristen feels so terrible, this is truly a nightmare for her, but there's nothing she can do to turn back time.
"If Rob takes her back at this point it will be a miracle, but she knows she only has herself to blame."
Stewart admitted she had cheated on Pattinson with Sanders - who has two children, Skyla, seven, and five-year-old Tennyson, with wife Liberty Ross - after pictures emerged of them kissing in a car and released a statement saying how sorry she was.
SANDERS WANTS RECONCILIATION AFTER TWILIGHT AFFAIR
Rupert Sanders thinks his affair with Kristin Stewart was the "worst mistake of his life".
The Snow White and the Huntsman director deeply regrets his secret relationship with the Twilight actress and fears it could have ruined his marriage to Liberty Ross, as the model continues to refuse to forgive him and was even spotted without her wedding ring in Los Angeles.
An insider told RadarOnline.com: "She is refusing to see him right now and has not spoken to him about if they have a future together or not.
"Rupert is willing to do absolutely anything and everything he can to save his marriage, he realizes this is the worst mistake of his life, and he cannot believe he was so stupid.
"The thought of losing his wife and children, who he loves more than anything in the world is killing him."
Liberty was pictured putting on a brave face as she stepped out without her wedding ring over the weekend for the first time.
The model - who has two children Sykla, seven, and Tennyson, five with Rupert - has reportedly not seen her husband since the telltale pictures emerged of him embracing the 22-year-old brunette, and the director is now worried a reconciliation is looking "increasingly unlikely".
The source added: "Liberty has told Rupert she just doesn't think she will be able to trust him again. This affair went on right under her nose and she feels like he has made her look like a fool.
"Rupert is just hoping it will blow over soon and he can win her back, but that is looking ever increasingly unlikely."