Einlion
Toga being a waifu candidate had fairly decent odds (though not that high; she is a psychotic villain that the other girls would need a lot of convincing to allow and probably hurt his rep with them for even considering it without a very convincing reason), and her showing up soonish was more or less certain, so it's not that shocking. That said, I certainly didn't think it would be this soon or in this matter. If I had to guess, I would've bet on her trying to impersonate one of his girls and him catching her with his observe or something.