Kardashian and Thompson even picked up the prize for best couple's costume, proudly showing off their trophy on social media.
Fans did notice that the 19-year-old, who was also sporting some lavish wings as part of her "good girl" look, strategically kept the camera focused on her face.
A pregnant Khloe Kardashian went out as Daenerys Targaryen, mother of dragons, and was accompanied by her National Basketball Association star boyfriend, who took on the image of Khal Drogo, leader of the Dothraki.
In a photo taken during an October trip to San Francisco, sisters Kourtney and Kim stood in a strategic position in front of Khloe, possibly to block any indication of a baby bump, People reports.
However, it was a glimpse of her stomach which caught most fans eyes on Instagram when she shared the snaps as Khloe wore a brown leather skirt and metal bodice.
'Marriage is definitely in the cards.
Let's all get checking out a bunch of times Kylie Jenner proved she was the Queen of selfies.
"Holy s-t. I'm like one of those fat kids that sweat when they get excited", Khloe says in the clip, turning on the air conditioning in the auto while eating pizza.
"This is such a wonderful moment for her, not only is she going to be a mother, she is going to be raising a child with a man she truly loves", the source added.
She's still taking extra caution not to show her pregnant belly to her fans.