Find out what will happen on your favorite shows, including ''How I Met Your Mother,'' ''30 Rock,'' and ''Grey's Anatomy"

TV fans no longer have to wait to find out what’s happening on their favorite shows. Twice a week,’s Spoiler Room ( has the inside look at what’s ahead.

Over six seasons, fans of How I Met Your Mother have clamored for clues about the mother’s identity, a mystery that likely won’t be solved for a while considering the comedy was recently picked up for two more seasons. The show’s second-biggest question, however — who is Barney’s father? — will soon have a definitive answer when John Lithgow guest-stars as Barney’s dad, Jerry, on two episodes of the CBS comedy. In March 21’s ”Legendaddy,” Barney (Neil Patrick Harris) shows up on his father’s doorstep, only to learn that his dad isn’t as awesome as he imagined. But Barney’s disillusionment doesn’t last long: ”This second episode is Barney trying to reawaken the beast within his father,” co-creator Craig Thomas teases exclusively to EW about the April 18 episode. ”His father used to be this badass, and that’s part of the reason he wasn’t there for Barney. They have a wild night together, but it has a very different outcome than Barney had hoped for.”

A Special Guest on 30 Rock

Move over, Bubba! Former president Bill Clinton won’t be showcasing his comedy chops after his people reportedly turned down a chance for him to cameo in 30 Rock‘s hour-long 100th episode. However, his loss is Michael Keaton’s gain! A source confirms the actor will return to his funnyman roots (Mr. Mom) and appear in the landmark episode, airing April 21.

Anna Faris on Parks and Rec?

Short answer: probably. Longer answer: if they can pen the perfect part. ”The writers are dying to work it out,” explains Anna Faris’ husband and Parks and Recreation star Chris Pratt. ”Megan Mullally came on as Nick Offerman’s ex-wife, and that’s going to be a tough act to follow.”

Grey’s Anatomy Finale Dish

Those anticipating another massive-disaster finale can stop waiting. That’s not to say viewers won’t walk away completely shocked, though. ”I expect to hear a lot this summer that I broke all my promises to my fans, but we’re talking about growth in tremendous ways for our characters,” hints creator Shonda Rhimes.