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Kourtney Kardashian, Kim Kardashian

Instagram

They're twinning!

Kim Kardashian appears in a rare selfie, posted on sister Kourtney Kardashian's Instagram page early Sunday, more than a month after she gave birth to her and husband Kanye West's son Saint West.

The two Keeping Up With the Kardashian stars are pictured in a studio, wearing what appear to be matching outfits—a long, tight long sleeve mock turtleneck and black leggings.

"Studio hoes. #SWISH," wrote Kourtney, 36.

SWISH is the name of Kanye's upcoming album. The 38-year-old rapper had also used the word on Twitter last March, alongside screenshots of Kim taking part in a nude photo shoot on the season 10 premiere of Keeping Up With the Kardashians

Kourtney also posted a selfie of sister Kylie Jenner, 18, standing in the same area and wearing a black Tommy Hilfiger fleece. The teen wears the same outfit in a recent Snapchat video.

"#SWISH," Kourtney repeated.

#SWISH

A photo posted by Kourtney Kardashian (@kourtneykardash) on

Kim, 35, has vowed to lose the weight she gained while pregnant with Saint, her and Kanye's second child. Kourtney has gradually slimmed down by working out and eating healthy since giving birth to her and now-ex Scott Disick's third child, son Reign Disick, who is now 1.

Since Kim and Kanye welcomed Saint on Dec. 5, the reality star has rarely been seen in updated pics, sharing mostly throwback photos. She revealed earlier this month she has gained 60 pounds while pregnant and has already lost 30 pounds but is still 40 pounds away from her goal weight. She also said she is teaming up with Atkins.

"Kim is staying on track with her weight loss progress and taking it day by day," a source recently told E! News. "She is very busy with Saint and North [West] in between of taking care of herself and being a wife."

Watch Keeping Up With the Kardashians Sunday at 9 p.m. only on E!