Sarah Chalke is going from "Scrubs" to "How I Met Your Mother" for the CBS comedy's increasingly star-studded Monday, March 24 episode.

That episode, the show's second in its new 8:30 p.m. time slot, will also feature the previously announced guest appearance by pop tart Britney Spears.

Here's what we know about the plot: Ted (Josh Radnor) goes to dermatologist Dr. Stella Zinman (Chalke) and begins falling for her. At the same time, the doctor's assistant Abby (Spears) begins falling for Ted.

At one point, the Stella character was speculated to be a possible multi-episode love interest for Ted and the Internet was abuzz that Alicia Silverstone would be taking the role. Instead, to accommodate Chalke's schedule, the character is now slated for only one episode.

"Not only is Sarah smart, funny and charming, but we already know she looks damn good in a lab coat," raves series co-creator Craig Thomas in a statement.

Thomas also has kind words for his other guest star, observing, "We're thrilled to have Britney Spears on the show. Britney is an exciting new talent and we can't wait for the world to meet her. Now if you'll excuse me, I have to go check out this 'Internet' thing everyone's talking about."

The admiration appears to be mutual with Spears saying, "Working at 'How I Met Your Mother' has been so terrific. Everyone, including the cast, the crew and the producers, has been wonderful and Abby is such a fun girl to play. I'm having a blast!"

"How I Met Your Mother" is spending another year on the bubble for renewal, which seems positive stable compared to the fate of Chalke's long-running comedy. Depending on who you listen to, "Scrubs" is either dead, renewed at NBC or heading over to ABC as we speak (recent rumors have pointed to the latter, though nothing is confirmed or official).

Other credits for Chalke include the well-received telefilm "Why I Wore Lipstick to My Mastectomy" and, of course, her turn as Second Becky on "Roseanne."