"He'll be our long guy in the bullpen for now," Royals manager Ned Yost said.
Gee was optioned to the Minors on May 31 after giving up 13 earned runs over 19 1/3 innings over four starts since joining the rotation in mid-May to replace a struggling Chris Young.
In seven relief outings to start the year, Gee had a 2.61 ERA over 20 2/3 innings, allowing just a .234 clip from opposing batters.
Alexander was called up May 12 and gave up seven runs in 13 innings of relief.
"He had options," Yost said of the decision to send Alexander down. "We wanted to protect our inventory."
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.