Emmy Award-winning actor Bob Newhart is returning to 'The Big Bang Theory' in its 12th and final season.

After appearing previously in 5 episodes of TBBT as Professor Proton, Newhart is back again to offer advice to Sheldon, who is having marital problems with his wife Amy, in the new episode titled 'The Planetarium Collision', set to air on Thursday. 

When Amy lacks time to work on super-asymmetry, Sheldon goes to great extents just so that she will be able to work with him, jeopardizing her in the process.

This leads to the first fight for the newly married couple, and Newhart appears to advise Sheldon on how to move forward in the marital conflict.

"Bob is back to offer advice because when you have marital problems you go to Bob Newhart. In a robe, in Jedi robes," Jim Parsons who plays Sheldon Cooper says in a video uploaded by Entertainment Tonight.

“I’m kind of Obi-Wan – whatever that means,” Newhart says with a smile to the camera. “Whenever Jim has a problem then he comes to me. He and Amy had a fight and he came to me and wanted my advice on how to handle their first fight.”

The other cast members were equally happy and excited to have Newhart back on the show. "I was so happy to see him when he got here," says Kaley Cuoco in the video.

Adding to what Cuoco and Parsons says in the ET clip, Melissa Rauch who plays Bernadette says, "Bob is just as amazing as ever. Even I was just marveling at the table read, his timing is just unbelievable to watch."

Apart from Newhart's appearance, 'The Planetarium Collision' will also witness Raj Koothrappali and Howard Wolowitz get into a tiff over hosting duties for a show happening at the planetarium.

'The Big Bang Theory' season 12 airs every Thursday 8 pm ET on CBS. Check your local listings for more information on the show.