Taylor Swift was surprised by a belated 30th birthday party in the recording studio on Wednesday (18.12.19).

Taylor Swift's birthday surprise (c) Instagram

Taylor Swift's birthday surprise (c) Instagram

The 'You Need to Calm Down' singer reached the milestone age on December 13, but a few days later, her collaborators Jack Antonoff and Laura Sisk hosted a small celebration to mark the occasion.

Taylor shared a photo of herself holding a birthday cake with Jack and Laura holding balloons either side of her and wrote: "Walked into the studio to a surprise birthday party from these two @jackantonoff & @sharp_stick - it's equally wild and cozy to think it was the three of us in a room making a song called Lover here last year. [heart emoji]."

The 'Cats' actress had marked her birthday with an "aggressive" festive-themed party with friends including Jack, Ryan Reynolds, Blake Lively, Martha Hunt, Camila Cabello, Halsey and Gigi Hadid - with a festive-themed bash, which took place after she'd performed at the Z100 Jingle Ball in New York.

She wrote on Instagram: "Honestly spending my 30th with the fans who have made my life what it is at jingle ball, then throwing the most aggressive holiday party known to womankind ... I just seriously feel so lucky for you all and will spend forever trying to find ways to say thank you. *cries in Christmas tree* (sic)"

Taylor previously admitted she is approaching her thirties with a healthier outlook.

Speaking before her birthday, she said: "I'm really excited about it. I've heard really good things about your thirties. Feeling a bit more secure ... a bit."

And the 'Me' singer believes her age has helped her to analyse "toxic messages" about her body and improve her relationship with body positivity.

She added: "One thing going into my thirties that I'm really stoked about is I now can really recognise and diagnose toxic messages being sent to me by society, by culture about my body. I'm a woman, I'm not a coat hanger. I need to feel healthy in my life, and I need to take pleasure in food, and I need to not use my body as an exercise of control when I feel out of control in my life."