Bieber and the Wizards of Waverly Place star are said to have separated as they struggled to spend time together.
"Because of their crazy schedules, it was getting harder and harder to maintain a relationship," a source told E! News. They added that the pair had broken up about a week ago.
Last month, Bieber hinted that the couple had gone their separate ways when he posted a moody black-and-white photo with the caption 'Lingse' on Instagram.
Fans of the star quickly pointed out that the word was an anagram of 'single', before Bieber deleted the picture and replaced it with a similar photo accompanied by the phrase "Just me".
Yesterday (November 9), rumours began circulating that the singer had openly flirted with models and asked for their numbers while backstage at the Victoria's Secret Fashion Show.
The 18-year-old performed alongside Rihanna at the lingerie presentation, before he was spotted in the audience at The Lion King on Broadway with 19-year-old Victoria's Secret model Barbara Palvin.
After Palvin and Bieber exchanged a number of tweets and photos, Gomez took to her account to post another photo of the pair, which she simply captioned "...".
Gomez and Bieber first went public with their romance in February 2011, when they attended the Vanity Fair Oscar party together.
As recently as September, they were rumoured to be building a house together, after Bieber's mother described them as "great together".
Watch the video for Justin Bieber's latest single 'Beauty and a Beat', which features a line about Selena Gomez, below: