One Direction mentor Simon Cowell has slammed his protege Niall Horan for alleged “lack of loyalty”.

Horan released his first solo single, This Town, under Capitol Records USA and not with Cowell’s Syco.  The latter released the previous LPs of One Direction.

This Town has ranked at number nine on the charts, eight places behind James Arthur. The former X Factor champion recently re-signed to Cowell’s label Syco and scored a comeback Number One hit.

His bandmates – Louis Tomlinson, Liam Payne, and Harry Styles – are all happy for Horan and they tweeted their support for him. However, Cowell is not feeling the same. The music mogul said: “He [Horan] probably would have had a number one single if he’d stayed with me. But you know who does have number one this week? James Arthur. Very pleased he’s back with us with a fantastic record.” Cowell then jokingly added an apparent diss at Horan – “hashtag loyalty”.

Check out the Niall Horan This Town video below.

Cowell formed and mentored One Direction fresh from their X Factor stint in 2010.  The boy band rose to popularity and has topped the charts since then. However, the group was reduced to four when Zayn Malik left his bandmates in March 2015.  The four remaining members released their first studio album, Made in the AM, late last year. The band then started their indefinite hiatus earlier this year.

Niall Horan is the first from the remaining 1D members to release solo material. Styles has announced he signed up for a solo deal with Columbia Records but is yet to release his first LP. In July, Liam Payne said he is going solo, too. Tomlinson has yet to announce his future plans.

Meanwhile, Niall Horan has also released a black and white video of This Town in a 1 Mic 1 Take promo that premiered on VEVO. The clip showed the pop heartthrob singing while playing an acoustic guitar.

The 23-year-old Irish singer co-wrote the track with long-time One Direction collaborators Jamie Scott, Mike Needle and Daniel Bryer. Horan recorded This Town with Adele’s producer Greg Kurstin.