The 34-year-old singer and the 'RIP' hitmaker ended on bitter terms almost four years ago, but it looks like the pair have finally buried the hatchet as the Scottish EDM superstar - who only follows 129 accounts - has befriended Rita and her new beau Andrew Watt on the photo sharing platform.
And it looks like the feeling is mutual as Rita and her partner Andrew followed back.
It's believed the pair settled their differences last year after they reached out to each other.
A source said: ''Late last year they got in touch and sorted things out. It was such a relief to both of them that they could move on and put things behind them.''
Rita was left heartbroken and embarrassed in the summer of 2014 when Calvin released a statement on Twitter announcing their split without pre-warning her beforehand.
A source said at the time: ''Rita was left embarrassed when he tweeted that it was all over. She didn't think he was going to make the announcement, so she was shocked.''
His announcement was short and nice, so it came as a surprise when he banned her from performing her track 'I Will Never Let You Down' because he had written and produced it.
That, in turn, meant Rita, 27, had to postpone the release of her fifth studio album because they had written and produced a lot of the songs together.
However, once they'd made amends, she was allowed to perform the track.
A source explained: ''Rita is now back in touch with a lot of Calvin's industry friends and able to work on music with them and, most importantly, able to perform 'I Will Never Let You Down'. She's gearing up for her second album soon and it's great to be able to perform arguably her biggest hit when she's doing promo for it.''
Rita has reportedly been dating Andrew since last year.