The 18-year-old boy is expecting a daughter in September.
And this afternoon, she went to Instagram to share the name she chose for her looming joy – Ophelia.
Millie revealed the unique name in a video showing her daughter’s name in beautiful, glittering silver letters with tiny pink bows.
A soft embroidered pink blanket can also be seen peeking out of some drawers.
She chose not to follow in the footsteps of mom Sue, 44, with an “e” at the end of all of her daughter’s names.
Millie’s brothers and sisters are Chris, 31, Sophie, 25, Chloé, 24, Jack, 22, Daniel, 20, Luke, 19, Katie, 17, James, 16, Ellie, 15, Aimee, 14, Josh, 12 , Max, 11, Tillie, nine, Oscar, eight, Casper, seven, Hallie, four, Phoebe, three, Archie, two and Bonnie, one and Heidie who is a few weeks old.
The couple’s 17th child, Alfie, was born in 2014.
Fans have described the name Ophelia as “beautiful.”
One of them said, “Yay so beautiful. I love it and I don’t know anyone with the name !! xxx ”.
Another added, “Aww is so unique. “
Millie announced her pregnancy in March and admitted she didn’t think getting pregnant “would be so easy” – despite her mother’s huge brood.
The teenager, whose six-month relationship with the baby’s father has ended, told The Sun: “We didn’t use protection. I knew there was a risk of pregnancy but I didn’t think it would be that easy.
“I didn’t worry about STIs because I trusted her. I had known him for years. “
Sue had her first baby – Chris when she was only 13 years old. She gave birth to her latest addition Heidie in early April.
Millie, who still lives in an overcrowded family home in Morecambe, Lancashire, added in March: “It is weird that my baby has an aunt who is only five months older. But that means they will hopefully be very close.
“My cycle is regular, so I knew I was pregnant. But I was afraid to find out for sure – and what mom would say.
“As“ two to three weeks into pregnancy ”broke out, I knew instantly that I was keeping the baby. My fear immediately turned into excitement. “
Millie admitted that her parents always saw her as the “good girl.” However, they were far from disappointed and absolutely delighted with the baby’s news.
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The teenager also says that she has a lot of experience changing diapers and transforming babies into small clothes.
Millie, who says the baby’s father is committed to caring for his child, is used to looking after his siblings, some of whom have had children themselves.