The singers have been pictured together on a number of occasions in the days following Selena's split from The Weeknd.
And now The Sun Online can exclusively reveal the pair are back together, after Justin's pastor Carl Lentz encouraged them to reunite.
A source close to the star said: "They started texting when she was in hospital for her kidney transplant. "Justin only found out through the press and he was hurt that she hadn't told him directly.
"He sent her flowers during her recovery.
"He has been going to church every week and spends all his time with his pastor Carl Lentz - Carl has been encouraging 'reconciliation' between the two - to heal their friendship at least - and Justin basically has been asking her for her forgiveness this whole time.
"He's really cleaned up his life majorly, they consider each other their one true love."
Justin regularly attends the controversial Hillsong Church, and The Sun Online previously revealed how all of the 23-year-old's potential girlfriends have to meet Carl to make sure they don't lead the former bad boy astray.
A source told us: "Justin does not make a move without consulting him.
"In the past Justin has been 'lead astray' or let's say gone off the rails behaviour wise in different relationships.
"Carl wants to help Justin rebuild his life in a solid way and the woman he is with - his romantic partner - has a big influence on him."
Fans of Justin will know just how much of an influence Selena, 25, has had on him over the years, ever since they first got together in January 2011.
Justin even got Selena tattooed on his arm, and when they first split in November 2012, the pair couldn't stay away from each other for long, reuniting and splitting up on a number of occasions over the next couple of years before officially splitting in 2014.
In November 2015, he tried to explain the dynamic of their on-off romance to Billboard, saying: "When you love someone that much, even if something comes between you, it’s a love that never really dies."
However the source added that while things are back on track now, it doesn't mean their future will be plane sailing.
They said: "It could still end though- they're both still so young and their history is so complicated."
A representative for Justin had no comment when approached by The Sun Online about the reconciliation.