The Big Bang Theory has enlisted the star of another huge nerd franchise to take on a major guest role in its final season.
Astin will play Dr Pemberton and Penn will take on the role of Dr Campbell, both physicists who accidentally confirm Sheldon and Amy's super-asymmetry theory.
This therefore confirms that the theory that the couple have been working on will reach a breakthrough in the final season that could potentially alter their lives.
Penn, meanwhile, has been playing Seth Wright in Designated Survivor, though is also well-known for starring in the Harold & Kumar series.
As The Big Bang Theory builds-up to its anticipated finale this year, its creator has admitted that bringing things to an end is "very, very sad".
"We’re coming up on Christmas break, we have one more episode to shoot before we break," Chuck Lorre said. "We definitely have discussed the finale. And we have a general idea of what we are aiming for with May and the finale.
"These days there’s a lot of melancholy in the background at all times. It’s been a 12-year project that has been really just a joy. It’s going to be very, very sad to let it go."
The Big Bang Theory airs on CBS in the US and E4 in the UK.
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