Since arriving on Earth, Mon-El has been harboring a big secret. He claims that he was a palace guard for the royal family of Daxam and survived his planet's destruction because the noble prince, who he was attempting to save, locking him in the one-man escape ship (a Kryptonian pod) and sent him away. It's a great story, but it sounds a bit fishy since Mon-El neither acts like a guard nor would you expect another alien race (end of the midseason finale) to travel the galaxy just to track down a mere Daxamite guard.
Many people, like myself, have a suspicion that Mon-El will turn out to be the Daxamite prince, but Executive Producer Andrew Kreisberg said, "No comment," when asked by EW. However, he did discuss how Kara will react to Mon-El's secret once he reveals it to her.
“Secrets are never healthy in a relationship and obviously Mon-El is holding onto something,” he said. “We got a little taste that his life on Daxam might not be as over as we think from the glimpse of the space farers, who are on the hunt for him. So it will definitely play a big part in their relationship moving forward.”
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Distributed worldwide by Warner Bros. International Television Distribution, SUPERGIRL is executive produced by Greg Berlanti (Arrow, The Flash), Ali Adler (The New Normal), Andrew Kreisberg (The Flash, Arrow) and Sarah Schechter (Blindspot, The Mysteries of Laura). Supergirl is based on the characters created by Jerry Siegel and Joe Shuster and appearing in DC Comics, by special arrangement with the Jerry Siegel Family.
Supergirl airs Mondays at 8 p.m. ET/PT; The Flash on Tuesdays at the same time; Arrow on Wednesdays and DC's Legends of Tomorrow on Thursdays. All four series air on The CW. The "Invasion!" crossover will air beginning November 28.