Lily Allen's Brother Alfie Welcomes His First Child, a Baby Girl, with Girlfriend Allie Teilz

Lily Allen is an aunt!

The singer’s brother Alfie, best known for playing Theon Greyjoy on Game of Thrones, recently welcomed his first child with girlfriend Allie Teilz. The actor, 32, announced the baby news on Instagram Monday with a photo of the newborn adorably gripping his finger.

“With full hearts and overwhelming joy @allieteilz and I introduce you to the newest member of our family,” Allen captioned the father-daughter photo. “She is perfect.”

Allie’s sister Mia also shared a photo of the couple’s child on Instagram. “Proud auntie moment my sweet libra niece + strong sister mama,” she said.

Neither Allen nor Teilz had previously announced a pregnancy before the arrival of their baby.

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.

The new parents were first romantically linked in June 2017 when they were spotted on a vacation together in Formentera, Spain.

Allen’s famous friends, including Olivia Munn and Samantha Ronson, congratulated him on his bundle of joy in the comments section of his post.

The news of Allen’s child comes after his sister Lily recently opened about his embarrassing meeting with the late Princess Diana in her new memoir, My Thoughts Exactly.

The meeting came at the 1991 London premiere of Hear My Song, a film produced by Allen’s mother, where the kids were tasked with greeting Diana with gifts. “Diana the Princess of Wales came to the premiere. I was a flower girl and gave her a posy, Alfie had a box of handkerchiefs to give her but somehow he got his k— caught in his trouser zip moments before meeting her,” Allen recalled in her book, according to the Daily Mail.

While Lily expertly handed off the flowers and curtsies, Diana showed concern for Alfie upon seeing the child crying. “‘Are you ok?’ she asked him,” Allen wrote. ” ‘No,’ he replied. ‘I’ve got my willy caught in my zip.’ “