Niall Horan spotted looking devastated after Liam Payne's tragic death in Buenos Aires

Niall Horan appeared heartbroken today, marking his first public appearance since Liam Payne's passing.

The 31-year-old former One Direction member fell 45 feet from the third floor into the courtyard of the Casa Sur Hotel in Buenos Aires, sparking an outpouring of tributes from the entertainment world.

Courtesy: MJ-Pictures.com

Horan, who had seen Payne perform in Argentina just days before his death, looked visibly upset as he walked through London with his girlfriend, Amelia Woolley.

The "This Town" singer, also 31, was spotted wearing a Muirfield Village golf cap, a green jacket, and dark sunglasses.

This sighting follows Simon Cowell, 65, being described as "shocked and devastated" by Payne's death, as he was also seen for the first time this afternoon.

Cowell was photographed in the back of a car in Blackpool, where he had been holding auditions for Britain's Got Talent before canceling the event upon hearing the news of Payne’s death.

Horan appeared solemn as he and Amelia took their dog for a walk in the park.

Meanwhile, police investigating Liam Payne's sudden death are searching for two "key witnesses" who may have been among the last to see him alive.

The singer died instantly from multiple injuries, which caused "internal and external hemorrhaging."

Argentine authorities are now looking for two women who were with Payne at the Casa Sur Hotel the night before his unexpected death.

Both women reportedly left the hotel the next day after waiting for Payne in the lobby, according to Argentine outlet 'Infobae'.

There is no suggestion that the women were involved in Payne's death, but investigators hope they can provide details about his final moments before he fell to his death around 5 p.m. local time.

Today, Payne's family expressed their heartbreak over his untimely death, stating that the former One Direction star will "forever live in our hearts."