Johnny Galecki will appear in an episode of the forthcoming Roseanne reboot.
"We have got our Johnny Galecki back on 'Roseanne' this episode - what a joy to work with such a deeply empathetic actor," she wrote, according to Entertainment Tonight.
"Very moving 4 all of us. #JOY."
Barr followed up by calling the new season "a dream come true." She also praised the young actors who will play her grandchildren on the show.
"this 10th season of 'Roseanne' is just a dream come true for an old lady comic who fought so hard 2 honor working class ppl in America," the star tweeted.
"the kids playing my grandchildren on the 'roseanne' show are fantastic actors and I am in love with all three of them. They r all movie stars!" she added.
Sources told ET Galecki is on set rehearsing this week and will film his episode Friday. The actor portrayed David Healy in Seasons 4 through 9 of "Roseanne's" original nine-season run.
ABC Entertainment President Channing Dungey had confirmed in August that Galecki, who now stars on CBS sitcom "The Big Bang Theory," was in talks to return.
The Wrap reported Nov. 13 that the actor had yet to finalize a deal.