11-year-old Irish girl joins Pentatonix for achingly beautiful cover of 'Hallelujah'

It was the song that shot Pentatonix to international stardom ... but prepare to hear the quintet take 'Hallelujah' to a whole new level with the help of an 11-year-old girl from Ireland.

Inviting Kaylee - who has ADHD and autism - to join them on stage, the Grammy Award-winning a cappella group absolutely wowed the audience with their achingly beautiful harmonies.

Unsurprisingly, Kaylee and Pentatonix received a standing ovation at the end of the spine-tingling performance.

So special getting to watch the young girl fulfil her dreams.