Mengden's contract was selected by the Royals on Monday.
Mengden joined the Royals on a minor-league deal in early March, and he posted a 5.47 ERA and 1.49 WHIP in 52.2 innings over 12 appearances (11 starts) at Triple-A Omaha to begin the season. The right-hander pitched in the KBO last year but will join the Royals' bullpen after Joel Payamps (undisclosed) was placed on the COVID-19 injured list Monday.