Who is the last team to lose a doubleheader during the season when they won a World Series?

You have to go back to May 1, 2004 when the Boston Red Sox lost a double header to the Texas Rangers. The finals were 4-3 and 8-5.

With the almost relegation of double headers to make up games, there are several seasons where the World Series winner didn't play any double headers. The rest of them since 2004 have either been split or swept by the eventual World Champion.

Interestingly, the day prior to the Boston-Texas games, they played a double header against the Tampa Bay Devil Rays winning both. Maybe they were worn out enough by Tampa that they didn't have enough left for the Rangers.