The couple posted snaps of the celebrations on Instagram on Friday (03Mar17), including pictures of the 23-year-old's personalised cake from the Womanizer hitmaker.

"My baby’s birthday," the 35-year-old singer captioned her set of snaps on the social media site, alongside a purple heart emoji. In the pictures, Britney is seen posing while on a hike with her boyfriend, and shared a photo of his cake. "Happy Birthday Hesam," the icing on the strawberry-topped creation read, in a nod to Sam's full name.

The birthday boy later gushed about the special cake from his pop icon girlfriend, sweetly captioning a shot of the sweet treat by writing: "She calls me by my real name."

The couple's romance began after they met on the set of her music video for Slumber Party last year (16), with Britney making the first move and asking Sam out nearly five months after they first met

"I kept his number, and it was so weird - it was like five months later, and I found his number in my bag," she told CBS Radio's Fast in the Morning With Nathan Fast back in January (17). "I was like, 'He is really cute. This guy is really cute'. So then I called him, and ever since then... he is just a really fun, funny person."

The couple was first seen together in November (16) and have since been spotted on dinner dates, attending friends’ birthday parties, celebrating on New Year’s Eve and marking Valentine's Day (14Feb17) in a $30 million (£24 million) Airbnb mansion.