The May 11 broadcast, which features Peters as Karen's (Megan Mullally) sister, is titled "Whatever Happened to Baby Gin?" In the episode, "Grace (Debra Messing) and Will (Eric McCormack) are excited about becoming parents to her baby. While Vince (guest star Bobby Cannavale) finds a beautiful brownstone that he and Will can live in, he doesn't see Grace as part of the plan. In the meantime, Grace learns some surprising personal news and the audience meets Ginny (Peters) — Karen's sister who was injured in a Twister accident when the two were kids."

"Will & Grace" airs Thursdays on NBC at 8 PM ET; the comedy concludes its eight-year run May 18 from 9-10 PM ET.

Bernadette Peters was last on Broadway in the acclaimed revival of Gypsy, for which she received a 2003 Tony Award nomination for her performance as Momma Rose in the Sam Mendes-directed production. She won her two Tonys for her performances in Andrew Lloyd Webber's Song & Dance and Irving Berlin's Annie Get Your Gun, and she has also starred on Broadway in Mack & Mabel, On the Town, Sunday in the Park with George, The Goodbye Girl and the original production of Stephen Sondheim's Into the Woods.

Peters' newest recording, "Sondheim, Etc., Etc.—Bernadette Peters Live at Carnegie Hall (The Rest of It)," hit stores on the Angel Records label last summer.

For more information visit www.nbc.com/Will_&_Grace.