Reynolds makes Family Guy cameo
The Green Lantern heartthrob plays the forerunner of Jesus in the episode, which features leading man Peter Griffin and wife Lois as Joseph and Mary.
In clips released ahead of the show airing, Ryan plays the first son of God, who wasn't as clever as his successor.
The Canadian star is also lending his voice to the animated film Turbo, which is currently being made.
The festive episode will air in the US on Sunday.