The twins, 45, who rose to fame as Jessica and Elizabeth Wakefield in the 1990s TV adaption of the Francine Pascal books, have shared Brittany's "modern day journey to parenthood" in a new interview with People in the US.

After undergoing treatment for stage four non-Hodgkin lymphoma, Brittany was told that, due to the intense chemotherapy she had received, conceiving on her own would likely be impossible.

So Cynthia donated her eggs.

After three unsuccessful IVF attempts, Brittany and her husband Adam Touni, a real estate broker, went down the surrogacy route, again using one of Cynthia's eggs - and baby daughter Hope was born in October.

Sharing a picture of the article on Instagram, Brittany said Cynthia had "helped make my dream come true of becoming a mom".

She continued: "My husband and I couldn't be more grateful to you sis. You're an angel. Thank you @people for sharing our modern day journey to parenthood."

Cynthia, who is now a photographer, told People: "I saw it as such a simple gift I could give to her.

"I know Brittany would do it in a split second for me. And we've always shared everything, so why not this?"

The twins found fame in Sweet Valley High, with Brittany playing the rebellious and outgoing Jessica, Cynthia the sensible and studious Elizabeth, but also starred in The Basketball Diaries together alongside Leonardo DiCaprio.

Brittany, who went on to appear in shows including Dawson's Creek and films such as White Chicks, told People about Hope's first meeting with Cynthia, saying: "It was so cool to see my sister with Hope for the first time because I'm like, she's your baby, too."

Cynthia said she wasn't sure how she would feel meeting Hope and wondered if "all these emotions [would] come up for me", but added that she feels just like her aunt.

Brittany was diagnosed with stage IV non-Hodgkin lymphoma - a type of cancer that develops in the lymphatic system, part of the immune system - in 2011, so Hope's birth has come after years of trying.

Cynthia is married to Yellowstone actor Cole Hauser and the couple have three children together - Ryland, 17, Colt, 13, and Steely, eight.