Little boy serenades his late sister with song from the movie Coco

A boy has serenaded his late sister Ava Lynn on what would have been her first birthday.

Alex Deais, 4, from San Antonio in Texas in the US, chose to sing the song "Remember Me" from the movie Coco as his parents watched on.

Ava Lynn died in May at just 4 months due to complications from hydronephrosis, a blockage in the tube that connects the kidney to the bladder.

The little boy didn't know he was being filmed by his parents who then shared the video on Twitter and it has since been viewed over 1.4 million times.

Alex's dad Samir shared the video on his Twitter account, writing, "My wife and were literally brought to tears seeing how much love Alex and Ava and our family has received.

"We were FLOORED last night!! I couldn't me more thankful. Thank you to everyone from our little family! What a 1st birthday baby girl!"

The family then re-tweeted the video, saying, "My son singing "Remember Me" from the movie "Coco" to his baby sister, Ava, who we lost this past May. He's only 4 years old and he understands.

"He didn't even know he was being recorded. He just wanted to sing to her for her 1st birthday!"

The family also shared they are expecting 'rainbow baby' whom they have already named Stella Grace.