Keenan will serve as Cherry's second-in-command for the next two years.
Also joining as executives producers are writers and former co-executive producers John Pardee and Joey Murphy who have been on the show since its first season.
The first part, "Something's Coming", aired on December 2, 2007.
Seven additional episodes were produced for the fourth season after the strike, the first of which aired on April 13, 2008.
Swimming for the California Golden Bears, he is a six-time NCAA individual national champion, winning the 100-yard and 200-yard backstrokes in 2014, 2015, and 2016.