Bara Caws administrator Linda Brown said she was "surprised but delighted" in securing the star's services.
"I never thought he'd say yes when I asked him to take part," she said. "I was really surprised but delighted when he agreed.
"He said he was absolutely thrilled to take part in our production and during the filming session he explained that it was going to see Bara Caws productions years ago that sparked his interest in the theatre and acting.
"I also think the prospect of appearing in the same production as his brother, Llyr, had something to do with it.
"Unwaith Unwaith is a lively, musical show for all the family."
The play, by Siundefinedn Summers, is an adaptation of the fairy tale, the Pied Piper of Hamlyn, and Llyr plays the part of the piper.
During rehearsals yesterday at the company's headquarters at Caernarfon, Llyr said he was looking forward to the tour.
He added: "It is the first time I have taken part in a Bara Caws production and it will be an experience that is bound to be very enjoyable. Being part of the show with Rhys is very much the icing on the cake."
