Bristol Palin Meyer celebrated World Down Syndrome Day on Tuesday with a sweet message for her 8-year-old brother Trig Palin

Bristol Palin Meyer celebrated World Down Syndrome Day on Tuesday by honoring her 8-year-old brother Trig Palin.

The 26-year-old reality star, who is approximately seven months pregnant with her third child, shared a gallery of sweet photos of her and Trig on Instagram.

“Trig continues to light up our world,” she wrote in a caption for a photo of her brother — who turns 9 on April 18. “He IS the boss around here and continues to fill our days with so much laughter! He is stubborn, and knows exactly what he wants – right this second.”

The youngest son of former Alaska governor Sarah Palin, Trig has “got everyone wrapped around his short chubby fingers,” Bristol said – especially her father “who constantly stops by his school to make sure that he ate his lunch, and that his face is clean.”

Bristol ended her tribute with an inspiring message of gratitude. “Trig is our definition of perfection and there isn’t one day that goes by without us feeling so thankful that God chose us to be his family,” she said.

She hashtagged the post, “#theluckyfew #mybrotherhasmorechromosomesthanyours #TrigPaxsonVanPalin”

In another Instagram post, Bristol can be seen reading books with her brother and her 8-year-old son, Tripp.

“Family time with my favorite little guys as we celebrate this World Down Syndrome Day,” she wrote.

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Bristol and husband Dakota Meyer announced on Instagram March 2 that they’re expecting a girl, their second child together. (Tripp’s dad is Palin’s ex-fiancé, Levi Johnston.)

“Dakota and Tripp officially outnumbered … so excited to let you all know, ITS A GIRL!!” Bristol captioned a photo of her and Meyer holding a white and pink “It’s A GIRL” sign.

She also shared two more snaps of the soon-to-be family of five, with Tripp showing off a “BIG BRO” sign and Palin and Meyer’s 1-year-old daughter, Sailor Grace, holding a “BIG SIS” sign.

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Last December, the couple revealed that they were expecting another bundle of joy in the spring.

“We are so excited to announce that our family is expanding!” they said in a statement. “God has blessed us so much; we are thankful for His grace and new beginnings. A springtime baby in the Meyer home and we can’t wait!”