Mom shares heartrending photos of three-year-old son comforting his terminally ill baby brother

At just four months old, he is already fighting for his life.

Thomas Blanksby was born with malignant rhabdoid tumour. His mom, Australian blogger Sheryl Blanksby, shared the heartbreaking details of his battle with the agressive cancer.

"The irony of life has hit my family so hard and everything doesn't make sense anymore,

the devastated mom wrote on her blog.

"It feels like only yesterday when I posted about giving birth to our Rainbow Baby Thomas and here I am writing about his imminent death."

Read more: Kids and cancer: what you need to know

On her Instagram page, she often posts pictures of her eldest, three-year-old William, comforting his little brother whenever he sees him in pain.

Sheryl once heard the little boy tell Thomas:

Sheryl and her husband Jon have not told William that his brother is dying. They've told the youngster his new brother has an "ouchie" and the doctors are trying to help.

"He is aware that Mummy and Daddy are very sad because Thomas is not well," they told DailyMail Australia.

"William also said that maybe the doctors can't help his baby brother, that's why Mummy and Daddy are sad. So we think he knows in his own way."

On Instagram, Sheryl added, "Watching my two sons together is a dream come true. Being a family of four has always been part of my day dreams. It's now my reality and it's trapped in this nightmare no family should be in."

Sheryl decided to share the family's struggle to "gain my prayer warriors to help me pray for him."

"And to know now that the whole world is praying for Thomas (or thinking about him) is just beyond amazing."

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Sources: MsCHIKEE Blog, MailOnline, Independent