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This just in: A Defamer operative on the Fox lot sent in a sighting of How I Met Your Mother's heavily stunt-casted Britney Spears, which includes a Defamer! World! Britney! Sitcom! Walk-On! Exclusive! description of what she'll be wearing in the episode:

Saw That Chick Who Used To Be Married To K-Fed on the Fox lot today for her How I Met Your Mother guest spot.

Smoking like a chimney, and cup of coffee in hand. Girl cleaned up nice for TV. They had her in this kind of flowery blue/turquoise dress, and a pair of glasses. Granted, she's nowhere near the level of sexy she once was, but compared to what we've seen of her lately, she was looking pretty damn cute. Come to think of it, she kinda looked eerily like every picture I ever saw of (pre-preggo) Jamie Lynn.

The highly stimulated guest star promises to lend the coasting series the kind of instant buzz-boost that, temporarily at least, might give it a much-needed edge in the ratings—particularly if CBS lends it their full marketing support as part of their much-touted Trainwreck Sweeps Week, along with Tara Reid's surprise cameo on The Big Bang Theory, where she'll reprise her Alone in the Dark role as brilliant archaeologist and museum curator Aline Cedrac.