Sarah Chalke and Josh Radnor in How I Met Your Mother by Monty Brinton/CBS Sarah Chalke and Josh Radnor in How I Met Your Mother by Monty Brinton/CBS

Hear that? It's the sound of fresh ink drying on Sarah Chalke's brand spankin' new How I Met Your Mother contract!

Sources confirm to me exclusively that Chalke has formally signed on to reprise her role as Ted's possible future wife in at least one additional episode. (I first reported on the Chalke- Mother negotiations back on April 10.) The Emmy-worthy Scrubs cutup is due back on the Mother set this week to begin work on this season's third-to-last episode.

Meanwhile, talks are continuing for Britney Spears to return as Chalke's loopy assistant, although my source insists no deal is in place. Yet. "The producers want her back," says the insider, "and hope she will return."

My prediction: The ink will be dry on that comeback in the next 48-72 hours.