The band released a new single, Lost Boys Ocean Park Standoff vs Seeb , in collaboration with Seen, in February, and followed up on Friday with a new single, If You Were Mine featuring Lil Yachty.
The couple unveiled their relationship on social media in February of this year, after months of speculation.
Cassandra seemed genuinely smitten with her girlfriend as she recorded her downloading and playing the new track.
Cassandra's late husband passed away last May after losing his battle to cancer.
Ronson wore a shirt with the new track's title on it, and the beauty entrepreneur wrote 'She's so cute' on the shared clip.