WATCH: San Antonio boy sings 'Remember Me' from 'Coco' for baby sister who passed away

SAN ANTONIO – A 4-year-old boy's sweet serenade to his baby sister who passed away at 4-months-old is filling people on Twitter with a whirlwind of emotions.

Samir Deais tweeted a video of his son Alexander strumming his toy guitar while singing Remember Me, a song from the Disney Pixar film "Coco," in front of a shelf dedicated to his baby sister.

It's been viewed more than 1 million times since it was posted on Dec. 30.

Deais said his son was singing for his sister Ava Lynn on what would have been her 1st birthday.

Ava Lynn passed away on May 1 after complications from hydronephrosis -- an illness that affects the kidneys and bladder.

"Her body just couldn't handle anymore," Deais said. 

Deais said his son Alexander "just wanted to sing for her and make sure that she is remembered and loved by our family forever."

"He's only 4-years-old and he understands," Deais wrote in his Tweet. "He didn't even know he was being recorded. He just wanted to sing to her for her 1st birthday!"

The Deais family saw "Coco" in theaters and was brought to tears by the movie. The film illustrates the significance of Dia De Los Muertos, following a young boy as he travels through the Land of the Dead to find his great-great-grandfather who was a famous singer.

Deais said the movie helped his son find a connection to his baby sister.

"(Alexander) understands that she has passed and is in heaven, he has seemed to grasp onto the reality of it in a very sweet and innocent way a 4-year-old should when it comes to passing away," Deais said. "And we have Coco to thank for that."

Reactions to Alexander's serenade poured in from across the nation.

One person wrote, "I vowed not to shed a tear in 2018. And here we are first day of the new year and my eyes couldn’t hold back."

Deais and his wife announced they are expecting a new addition to their family -- Stella Grace Deais. Of course, Alexander was overjoyed to know he would have another little sister.