Tom Mann, who is from Southampton, found fame as part of the English-Irish boyband Stereo Kicks on the 2014 series of singing competition.
In an Instagram post on Monday, Mann said he was ‘completely broken’ after his fiancee Danielle Hampson died on the morning of the couple’s wedding day.
Alongside a picture of her and the couple’s young son Bowie, Mann wrote: ‘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.’
He continues: ‘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.
‘The most beautiful person inside and out. The most incredible soul. 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.’
Among the thousands of messages left on the post were comments from Scottish singer Capaldi, 25, who wrote: ‘Love you brother,’ followed by a red heart emoji.