R&B star Miguel is engaged to his model girlfriend Nazanin Mandi.

On Monday (11Jan16), the Adorn singer's longtime love sparked speculation she is heading down the aisle by posting a selfie on Instagram.com, subtly showing off what appeared to be a massive diamond engagement ring on her left hand.

A source tells E! News the engagement rumours are true, and that 30-year-old Miguel's proposal was "very heartfelt and real" and "done perfectly".

The insider adds, "Nazanin and Miguel are really excited to get married! They've been together for some time and knew that they were going to spend their lives together... All of their friends and family think they are the best couple and really complement each other."

Miguel and Nazanin have been dating for the past 12 years and his fiancee hopefully doesn't have a problem with some of his more sexually explicit lyrics in his songs.

The star previously revealed how women aren't offended by his honesty when it comes to his music, particularly a track called The Valley from his third album, which expresses his feelings about various sex acts.

"If you're not in a relationship, it's the epitome of everything you would want to say," he told Britain's Shortlist magazine. "I just say what I feel, and I've always been good at saying it the way we want to say it, as men. Quickie is a good reference for that, on my first album - it was a more playful way of saying it, less animalistic or visceral. "I'm saying what we want to say, and it comes across as real, so women aren't offended by it. It's like, 'At least he's being honest.' They just want to hear it the way it is. Sometimes it's maybe brash, but at least you can respect it."