Mac Miller. (Photo by Owen Sweeney/Invision/AP, File)

Mac Miller raps about his "personal demons" on a new track with Seth Hirsch.

The late rap star - who died of a drug overdose in September - posthumously appears on the track "Say Goodbye", which Seth says offers a "window into Mac Miller's soul".

Mac raps: "Living with a heart that's broken/ We know how that feel/ We always caught up in the moment/ And this ain't no drill, one shot one kill/ Just pop one pill, you'll be good by the morning."

Seth's perception of the track - and of Mac's verse, in particular - has changed since the rapper's death.

He shared: "The song's about toxic relationships, and dealing with someone who's s***ty towards [you], sucks up all your energy, and keeps taking advantage of your time and emotions.

"After Mac passed away, I realised this song was about a lot more than that."

Seth thinks the record will give fans an insight into Mac's pain prior to his death.

He told Complex: "It's really about struggling to say goodbye to our personal demons and the chains they put on us. ... This song is such a window into Mac Miller's soul and what he was going through."

The release of 'Say Goodbye' comes shortly after Ariana Grande expressed her anger that Mac didn't win a Grammy Award at the recent awards bash.

Ariana - who began dating the late star in August 2016, before they split in early 2018 - tweeted "f**k" and "trash" when Cardi B won Best Rap Album for 'Invasion of Privacy'.