Eagle-eyed Supergirl viewers (and people who watch previews for new episodes) probably put together the puzzle of Mon-El's (Chris Wood) secret identity ages ago, but Supergirl (Melissa Benoist) herself only just discovered that her boyfriend lied about his royal parentage in Monday's "Star-Crossed," when his totally not dead parents, played by guest stars Teri Hatcher and Kevin Sorbo, arrived on Earth.

Mon-El's decision to lie about being the prince of Daxam all those months ago naturally put his fledgling relationship with Kara on the rocks (again!), but it wasn't just that Mon-El lied to Kara about who he really was that upset her -- it was the fact he was perfectly willing to waste the opportunity of a second chance with his parents.

For someone like Kara, whose ultimate dream is to reunite with her own parents and bring Krypton back to life, it was incredibly frustrating to see Mon-El turning down the chance to reclaim his crown, be with his parents and give Daxam another chance at thriving. Even after Kara's stirring speech about second chances, he opted to forgo leaving with his parents -- and thus turned down the opportunity to be a prince -- in order to be closer to Kara, whether they were together or not. (Knowing what we know about the roles Mon-El's parents are supposed to play in the season-long story, combined with the looks on their faces after Mon-El's declaration, has us thinking he might come to regret that decision later on.)

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The more important thing to take from that scene, though, was how much Kara has changed Mon-El in just a short amount of time. There's still a lot of work to be done, sure, but he's become a much better person under Kara's influence, and Mon-El prefers that person tenfold to the selfish prince that he was back on Daxam. He wants to stay on Earth and help people rather than return to exploiting his people for the royal family's personal gain. Mon-El just needs to find a way to show Kara the progress he's made.

Teri Hatcher, Chris Wood, Kevin Sorbo and Melissa Benoist, <em>Supergirl</em>Teri Hatcher, Chris Wood, Kevin Sorbo and Melissa Benoist, Supergirl

Ultimately, Kara couldn't deal with the fact that Mon-El was able or willing to lie to her all those months. His answer was also less than satisfactory when she pressed him on whether he ever planned to tell her the truth. He tried to convince her that he loves her -- no, seriously, he said it three times -- but it wasn't enough. Kara was too hurt to see what Mon-El was trying to offer and she ended their relationship.

But Mon-El wasn't the only person revealed to be a big fat liar in Monday's episode. Winn's (Jeremy Jordan) girlfriend Lyra was revealed to be an art thief. At first Winn couldn't deal with the hurt, but when he found out Lyra was stealing art under duress to save her brother, he was willing to forgive her and push forward. It seems like Kara might need to try harder to see Mon-El's situation from his perspective. If she does, it might help them get back on track.

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Of course, there are bigger fish to fry at the moment. The Music Meister (guest star Darren Criss) arrived at the closing of the episode and put Kara in a trance that officially kicked off the Supergirl and The Flash musical crossover, which continues Tuesday night. Kara will have to find her way out of the Music Meister's spell before fans can hope for her to reconcile her relationship with Mon-El.

The Supergirl and The Flash musical crossover airs Tuesday on The CW. Supergirl continues Mondays at the same time.

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