Both were formed on Syco label boss Simon Cowell's talent shows, in the UK and US respectively, and the British stars have admitted they were like, 'Oh no!', when Fifth Harmony signed up to the label after coming third on the competition in 2012, just a year after Little Mix formed across the pond.
However, the 'Break Up Song' hitmakers - Jesy Nelson, Perrie Edwards, Jade Thirlwall and Leigh-Anne Pinnock - insisted they love 5H and never saw them as rivals because their music is so different to what they do.
Asked in a game of 'Truth or Wine' on BuzzFeed if they ever felt rivalry with Fifth Harmony, Jesy said: ''I'd say at one point we did.
''We can say that.
''We always loved them.
''We never didn't like them as people....''
Jesy then suffered technical problems and Perrie picked up: ''There wasn't rivalry as such because we loved them all, and we did like Fifth Harmony, but do you mean that when they came out we were a bit like, 'Oh no!'''
Jesy replied: ''Yeah.''
And her bandmate continued: ''Yeah, I don't think there was ever rivalry because they were so different.
''I think if they were doing the same stuff we were doing and we were similar, I don't know, but I feel like we never really thought that there was rivalry.''
Jade then added: ''No, I don't think we had a problem with the girls, I think it was more a bit awkward that we were on the same label more than anything.''
They all agreed in unison: ''Yeah!''
Fifth Harmony - which comprises Ally Brooke, Normani, Dinah Jane and Lauren Jauregui, and previously Camila Cabello until her departure in 2016 - have been on an indefinite hiatus since 2018.
Little Mix departed Syco before the release of heir 2018 LP, 'LM5', and Jade recently admitted the split from the music mogul ''f***ed [them] over'' and made it ''harder'' for them to channel their ''creativity'' into the record.
The 'Woman Like Me' hitmakers are now signed to Sony's RCA Records and are feeling much more positive about their future.
Quizzed on the lack of female empowerment in their music videos, Jade told The Sun newspaper's Bizarre column: ''We did a little bit but we had a switch of labels during the 'LM5' process and that really f***ed us over.
''It was harder to put all our creativity out there in the way we would have liked.
''The 'LM5 album' was very heavily on women's rights and our experiences in the industry.''
Lana Del Rey takes her 60s vintage aesthetic to the extreme with the video for new single 'Chemtrails Over The Country Club'.
As negotiations continue, it's clear that the UK government doesn't have everyone's best interests at heart.
The singer awkwardly responded to potential backlash regarding her new album cover.
Five years ago, on the day of his 69th birthday and two days before his death, David Bowie released his 25th, and final studio album, 'Blackstar'.
Nobody is impressed by Demi "coming to the rescue".
Let's leave gatekeeping in 2020.
These are the albums we're looking forward to most this month.
David Bowie poses difficult questions about lack of racial diversity on MTV.