as we know in sbs 83 oda confirmed that viola and doffy were “lovers” ( likely doffy forced himself on her / raped her)
SBS, Volume 83
“Q : I love Dressrosa arc and re-read again and again, but there is one thing I can’t understand enough.Why did Doflamingo and Viola call each other “Doffy” and “Violet” in chapter 788 where Viola confronted Doflamingo? What did they think at that time?
Oda : Actually there is a profound setting about it, but I’m afraid I can’t tell you. I told my editor about it, though.Considering ONE PIECE is Shonen manga, I’d like to hide it since the reason is for adult audience. Dressrosa is a nation of passion, indeed!!“
not to mention the recent vivre card databook
and as stated by other people there were hints and foreshadowing to that
viola was nicknamed ane-san which means older sister in japanese but The word is used by yakuza henchmen for their boss’s mistress and viola in chapter 712 was called ane-san by doffys henchmen.
onee chan means big sister and is used in the way you expect in the sense of actual family. there are a multiple yakuza terms which when translated to english you it means a familial term like pops or uncle
(the japanese word oyajii which the whitebeard pirates use for whitebeard isnt the yakuza term for pops its the actual japanese word used in familys for your fathers
orgcrime.tripod.com/japgangint . htm sanjivb . com/_site/archive/crime/yakuza_wives/index . php (look up ane-san in those posts
not to mention at how the beginning of the arc there was a line about women stabbing their lovers because of how passionate they are and viola tried to stab him
in sbs 90 when oda got the question about whether or not doffy, mihawk, or crocodile had children he didnt say no or that none of them arent expecting one.
so its possible that viola is pregnant with doffys kid and given that oda mentioned viola and doffy having a relationship to the point of having doffys men refer to her as his mistress it will be an interesting way to reference the relationship in the one piece manga
Oh boy, that's a daring claim! But following the hints you posted, it is possible :')