The 'Pray' rapper and the 21-year-old model were spotted getting intimate at Coachella Valley Music and Arts Festival's Poppy nightclub pop-up area in Indio, California, on Friday (13.04.18), where they were said to be ''all over each other''.
An onlooker told PEOPLE: ''The Weeknd and Bella were sitting on each other's laps and all over each other all night long. They definitely looked like they were fully back together.''
An insider says the pair have been ''secretly seeing each other recently'' after splitting up in 2016.
They told E! News: ''Bella never really lost feeling for Abel and had hope they would eventually get back together.''
However, they are yet to put a label on their relationship, as The Weeknd - real name Tesfaye Abel - has been ''playing the field'' and ''openly dating'' following his break up from Selena Gomez in October last year.
According to another source, Bella - the younger sister of Gigi Hadid - ''wants to be exclusive'' with the rapper.
They added: ''They are just getting back to a good place. She loves hanging out with Abel and they always have fun together and is very hopeful of their future relationship.''
In February, sources claimed that whilst The Weeknd and Bella weren't dating, it was ''only a matter of time'' before they gave things another go.
They said: ''It's only a matter of time that they get back together ... That has definitely not been ruled out ... They know it's all about timing ... When they are both ready to get back together, they will.''
The 28-year-old star was ''hit really hard'' by the news that his former flame Selena had rekindled her romance with ex-boyfriend Justin Bieber after her split from the 'I Can't Feel My Face' singer, and after spending some time recollecting his thoughts, he's said to be ready to move on.
The insider added: ''The whole Selena and Justin thing hit The Weeknd really hard ... After they got back together and that finally set in, he wanted to go dark for a bit and keep a low profile. He had his phase of going out and partying, but then really started to miss Bella again. They definitely still keep in touch and they still totally love each other.''
His new album Underneath It All is out now.