Selena Gomez and One Direction's Niall Horan were spotted on a date earlier this month - is her ex boyfriend Justin Bieber jealous of the potential new relationship, and refuses to invite her to his 20th birthday this weekend?

Though Niall Horan's rep says that the One Direction singer and Selena Gomez are not dating, it's impossible to ignore the photos of them hanging out in London together. When Selena visited the city, Niall reportedly took her out to dinner at Nando's restaurant.

Since their date, the pop singers have "been in constant contact since she went back to the States," Cambio reports.

A source told Heat magazine, "Niall's always fancied Selena, and he's made no secret of it. So when he went to Taylor's gig at the O2 London on 2 February he talked to her about setting them up."

The insider added, "He's just split from Barbra [Palvin] and Selena's trying to get over Justin [Bieber] so it's perfect timing."

But now news is coming out that Selena Gomez's ex boyfriend Justin Bieber is not inviting his ex girlfriend to his 20th birthday party this weekend. Is the "Boyfriend" singer jealous of Selena dating Niall Horan?

Hollywood Life claims a source said: "Justin is planning a huge party for his 20th birthday and he has not invited Selena. He does not want her there after she dissed him by hooking up with Niall, which was not cool according to Justin."

"There will be plenty of hot chicks there, and let's just say lots of party favours," the source went on, "It's going to be off the hook."

According to Hollywood Life, Selena does have a thing for Niall, but her history with Justin Bieber could be the reason things can't get serious right now.

"Selena likes Niall, but it's a case of Selena knowing that he likes her a lot and she wants a guy who plays hard to get or unattainable, which is basically not Niall and is Justin," the source said. "Her friends want her to give Niall a better chance and since she never ultimately listens to them, it just makes the seriousness of the relationship a major work in progress."

But Niall could be a great change for Selena, as the Heat source explains: "Niall's exactly the kind of guy [Selena] needs right now. He's so sweet, a total gentleman and 100 per cent not a player like Justin turned out to be."