Pop star Ariana Grande has gushed about her "soulmate" Mac Miller to celebrate the rapper's 25th birthday.

The Bang Bang hitmaker took to Instagram on Thursday (19Jan17) and shared a sweet message dedicated to the birthday boy, showing fans just how happy she was to call Mac her man.

Alongside a Snapchat video clip of the couple dancing in a car, she wrote, "Happy birthday to my best friend for life / soulmate @larryfisherman. I love you with all my heart."

The post wasn't all lovey dovey - Ariana used one of the app's face-altering filters to give them both exaggerated sad pout looks with big eyes.

The singer has clearly fallen head over heels for Mac since they started dating last summer (16).

The artists had previously collaborated on her 2013 track The Way, and teamed up again last year (16) for the song My Favorite Part, from the hip-hop star's recent album The Divine Feminine.

They have since shown off their love for one another in cute posts on social media, and in September (16), weeks after going public with their romance, Mac admitted he was "in love" with "amazing" Ariana.

Asked how the media attention affected their relationship and work, Miller told New York radio show The Breakfast Club, "Just because we are two people who are in love and have a great relationship doesn't mean I am going to get weird about this incredible music we make."

Meanwhile, the 23-year-old beauty has also started to open up more about their relationship, after initially refusing to confirm or deny they were an item.

Discussing the couple's ideal date night, she previously told Entertainment Tonight the pair enjoys "chill" time together.

"Like, random adventures," she shared. "Going on drives, looking for Pokemon, going to cute movies, making music."

"Every day (with Mac) is super exciting," she continued. "Just waking up and being like, 'Hell yeah!' Do you know what I mean? It's great."

Ariana previously dated former The Wanted singer Nathan Sykes, rap star Big Sean, and dancer Ricky Alvarez.