'This is Us' season 1 episode 9 spoilers: 'AHS' vet Denis O'Hare to play William's friend; Rebecca's betrayal to be explored

Following his mother's betrayal, things will get more painful for Randall (Sterling K. Brown) in the upcoming episode of NBC's "This is Us" season 1.

Fans' hearts were all shattered when last week's Thanksgiving episode saw Randall finally discovering that his mother Rebecca (Mandy Moore) had known his biological father William (Ron Cephas Jones) since Randall was born.

According to TV Guide, tonight's episode will get more emotional as it will reveal how and when Rebecca sent the letter with Randall's picture to William. They actually met again, and their second meeting will be more distressing. By the end of the episode, Rebecca's motives for keeping William a secret from her son will also become clearer. However, they are not enough to justify what she did to Randall.

It was previously revealed that "American Horror Story" vet Dennis O'Hare will be joining the show. The actor will play the role of Jessie, William's friend he first met in Narcotics Anonymous. He will make his debut on next week's episode "Last Christmas" and despite being just a friend of William's, his role is very significant because he gives viewers a glimpse of William's life before he reunited with Randall.

"He's a guy who allows us to learn more about William's old life before Randall (Sterling K. Brown) had come knocking on his door," series creator Dan Fogelman recently told Entertainment Weekly. "He's a friend from back before. And William on Christmas Eve returns home to take care of some stuff back at home, and through his old buddy, we get to learn more about William. It's not what the episode is about, but because people have been asking, he holds the answer to what has happened to William's cat."

"This is Us" season 1 airs every Tuesday night at 9 p.m. ET on NBC.