• ‘This Is Us’ Season 1, episode 12 promo, spoilers: What happens in ‘The Big Day’?

‘This Is Us’ Season 1, episode 12 promo, spoilers: What happens in ‘The Big Day’? (Photo : YouTube / Television Promos)

The list of guest stars on "This Is Us" is growing. The Mandy Moore-starred series has recruited Dennis O'Hare from "American Horror Story" and Jimmi Simpson from "Westworld" to appear on its freshman season.

O'Hare, who's known for being a major player in multiple seasons of "American Horror Story," was booked to appear in multi-episodes of "This Is Us." According to Entertainment Weekly, O'Hare has been tapped to play Jessie, a character who is a friend of William (Ron Cephas Jones). O'Hare will make his debut on the NBC drama later this season.

Like Us on Facebook

No word yet if O'Hare's character will be interacting with William's biological, son, Randall (Sterling K. Brown). In addition to his "American Horror Story" credit, O'Hare has also appeared on "The Good Wife," "The Comedians," "Banshee" and "True Blood."

As for Simpson, the actor will be seen with Brown's character in an upcoming episode of "This Is Us." According to Variety, Simpson will be introduced as Andy Fannan, a successful Wall Street trader who works with Randall. Simpson will only appear for at least one episode this season.

The airdate for his episode has not been announced.

Simpson's recent TV credits also include "House of Cards," "The Newsroom," "It's Always Sunny In Philadelphia," "Person of Interest," "Hap and Leonard" and "Psych." On films, he has starred on Steve Carrell and Tina Fey's comedy "Date Night," "White House Down" and "Zodiac."

Created and executive produced by Dan Fogelman, "This Is Us" has established itself as one of this year's breakout TV series. It also stars Milo Ventimiglia, Justin Hartley, Chrissy Metz, Susan Kelechi Watson, Chris Sullivan and Ron Cephas Jones.

Recently, NBC granted the show a full-season pickup following a strong series premiere this fall. Its freshman season, which was initially ordered with only 13 episodes, will now run with a total of 18.

An all new episode of "This Is Us" airs every Tuesday at 9PM on NBC.