The former is made up of people who were caught up the attack past year, while the latter saw their post-attack tribute - a version of Ariana Grande's My Everything - go viral and earn them the chance to perform with the star at the One Love Manchester concert.
The pop star tweeted early Tuesday morning that she was thinking of the survivors and the families of victims.
"I love you with all of me and am sending you all of the light and warmth I have to offer on this challenging day", she wrote. The event will include renditions of Grande's "One Last Time" and "Look Back In Anger" by Oasis, which became an unofficial anthem of Manchester after the bombing.
Twenty-three people including the attacker were killed in the terror attack at an Ariana Grande concert. To cheers, Manchester United great Ryan Giggs said: 'Manchester is a city of music and is a city of love, and we are sending out love and prayers on this emotional day'.
Those working on building sites across Manchester city centre found a unique way to observe today's one minute silence. "It will also give thanks to emergency workers who assisted on the ground and in the aftermath of the attack".
"All of you - and many more in this great city - are the very best of what this country stands for".
The commemorations began in the afternoon when Prince William and Theresa May attended a remembrance service at Manchester Cathedral, and were joined by the families and friends of those killed.
On the altar stood 22 lit candles, made from the wax of thousands of candles left in the city's St. Ann's Square in the days after the attack. The Lord Mayor of Manchester, June Hitchen, and the Bishop of Manchester, the Right Reverend David Walker, were also part of the event.
Around an hour and a half later, at 10.31pm, bells on Manchester Town Hall, St Ann's Church, and St Mary's RC Church rang to mark the time the bomb went off one year ago.
Prince William and the Prime Minister privately met bereaved families at the cathedral following the service and both attached notes to one of the Trees of Hope, a trail of small Japanese maple trees from Victoria Station to St Ann's Square, to add to the many thousands of similar messages of support and hope left by members of the public.
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