How does Selena Gomez truly feel about not being invited to ex-boyfriend Justin Bieber's 21st birthday party over the weekend?

The Canadian pop star rented out an entire private island near Grenada to celebrate his big 21, TMZ reported. 

A source revealed to HollywoodLife.com that Gomez did not expect an invitation from Bieber, so she was not upset at all. 

"Selena pretty much knew that she was never going to get an invite to Justin's 21st birthday party," the source said. "But she wasn't downhearted by it – she's moved on with Zedd, an older boyfriend, and is enjoying the most grown-up relationship she's ever been in. There is no drama – like with Justin – and it's all very easy."

Also, the "I Want You to Know" singer could not care less about the "Baby" hitmaker popping champagne with his former flames, Hailey Baldwin and Yovanna Ventura.

"Selena doesn't really care who Justin hangs out with and wasn't surprised that Yovanna and Hailey were at the party," the source said.

A HollywoodLife.com source said Bieber is finally moving on from Gomez for good.

"He knows that the relationship was not right for both of them, and he just needs to shy away from everything that isn't a positive thing in his life right now," an insider said. "If Selena ever needs Justin, however, he'd be there for her because he only wishes the best for her."

The insider added Justin Bieber's main focus now is his music career. The artist is supposedly writing new music every night. He is working on his next album, which is expected be produced by a couple of renowned hitmakers.

"Justin has been talking and meeting with Kanye West about producing some songs on his new album. He has also been working a lot with Rick Rubin," a source said. "If it was up to Justin, he'd be touring tomorrow."