Mann appeared in the eleventh series of The X Factor in 2014, finishing in fifth place as part of boyband Stereo Kicks, a group formed on the show, before going on to work as a songwriter for artists including Lewis Capaldi, Rita Ora and Tom Grennan.

He and his fiancée Danielle Hampson, mother to their eight-month-old son, Bowie, were due to marry on Saturday.

Writing on Instagram, Mann said: "I can't believe I am writing these words but my darling Dani - my best friend, my everything and more, the love of my life - passed away in the early hours of Saturday morning, 18th June.

"On what was supposed to be the happiest day of our lives ended in irreversible heartbreak. I feel like I have cried an ocean. We never made it to the alter; or got to say our vows, or dance our first dance, but I know you know that you were my entire world and the best thing that has ever happened to me, Danielle. I will wear this ring that I was always supposed to wear as a sign of my unconditional love to you.

"I am completely broken trying to process this and I honestly don't know where to go from here, but I do know I need to use any strength I can muster for our little boy. I will not be a mark on the parent that you had already become but I promise I will do my everything to raise Bowie just the way we always wanted. I promise you he will know how amazing his mummy was. I promise to make you so so proud."

Mann went on to describe his fiancée, who worked as a PR executive and a dancer, as "the most beautiful person inside and out" and "the most incredible soul".

He continued: "We have lost such a special person and I am sure we are about to see an abundant outpouring of love that reflects that. I will try to find peace in your messages and comments, but right now I am grieving and I will be for a very, very long time.

"My darling Dani, the brightest light in any room, my world is nothing but darkness without you. I will miss you forever."

Mann did not say how Ms Hampson died.

Ms Hampson danced on tour with the Spice Girls.

The group wrote on Twitter: "We were very saddened to hear of the passing of Dani Hampson who was part of the Spiceworld 2019 family. Sending love and strength to Tom, Bowie and Dani's family and friends."

The group's Emma Bunton wrote: "Heartbroken for you. A beautiful soul that will live on. Thinking of you all."

Other stars including Nadine Coyle and Capaldi were also among those paying tribute and sending their love to Mann following his post.

"Sending so much love, light & healing to you, Bowie & everyone who loved Dani!!" wrote Coyle, while Capaldi said: "Love you brother."