A surrogate mum has given birth to her own granddaughter aged 51.

Julie Loving stepped in to help her daughter Breanna Lockwood, 29, after she suffered heartbreaking losses and IVF failures.

She and husband Aaron, 28, thought their dreams of a family were doomed to failure after four years trying to have a baby, the Mirror Online reports.

But her fit and healthy mum, who has run 19 marathons, saved the day after offering to become their surrogate.

On November 2, Julie gave birth to Briar Juliette Lockwood — her own granddaughter.

New mum Breanna, from Chicago, Illinois, shared the news on her Instagram, writing in a post that the baby girl “has filled our hearts with so much joy".

Julie Loving has given birth to her daughter Breanna Lockwood and son-in-law Aaron's baby

“My mom was an absolute rockstar through a difficult delivery,” she wrote.

“The sacrifices she took to bring this little slice of heaven into our world takes my breath away. Holding my daughter in my arms my heart is bursting.

"The feeling of how I would do absolutely anything needed for this child is radiating through me when I look at her, and reflects back on what my mom did for me.

Julie stepped in after her daughter Breanna struggled to have a baby for four years

“Every move and decision I make for my daughter, I’m finding the answers through how my mom raised me.

"The way she loves and the selflessness she exudes is pure, genuine and kind.

"My mom Julie, and baby Briar are doing fantastic and healthy! I have SO MUCH to share on our birth experience, but right now my husband and I are soaking up these newborn moments!”

On November 2, Julie gave birth to Briar Juliette Lockwood — her own granddaughter

Breanna has documented her family's experience on her Instagram account ivf.surrogacy.diary, which is followed by nearly 150,000 people.

She wrote in an Instagram caption last week, alongside a picture of herself beaming as she gazed at her newborn: "Just living in new mama bliss!"

Speaking to Good Morning America earlier this year, the mother and daughter said they both desperately wanted the baby in their lives.

Breanna is overjoyed and says her mum is an 'absolute rockstar'

Julie was eager to become a gran and to help her daughter at the same time.

She told the TV breakfast show hosts how she was the one who suggested she be Breanna's surrogate.

Julie said: "I started to talk to her about it. She was not on board and thought I was crazy, but I just kept pursuing it.

"I've run 19 marathons and done many triathlons. I felt like health-wise I could do it and I had really easy pregnancies with my two kids."