The Princess of Wales planned her carol service with help from the grieving Lady Gabriella Windsor whose husband was found dead earlier this year.
Kate invited Lady Gabriella during the summer to join her team organising her annual Together at Christmas event at Westminster Abbey which featured a host of stars.
A source said about Lady Gabriella: “She was very touched and grateful to the princess to be asked to contribute to her very special concert, and that she felt honoured to do so.”
Kate is understood to have been incredibly grateful for her contribution.
A coroner concluded in October he took his own life and during the inquest his widow warned about the effects of drugs used to treat mental health problems after the hearing was told Mr Kingston was prescribed drugs following complaints of trouble sleeping following stress at work.
Lady Gabriella, also known as Ella to her friends, supported Kate and played an advisory role with the organising team around the music performances that featured during the service.
Kate and William were joined by their children Prince George, 11, Princess Charlotte, nine, and Prince Louis, aged six, who all held candles during the service, as did the other guests who included members of the monarchy.
Olympic cycling champion Sir Chris Hoy, who is terminally ill with prostate cancer, lit a candle as did Lindsey Burrow, the wife of former rugby league star Rob Burrow who died in June following a much-publicised battle with motor neurone disease.
Readings were given by actors Richard E Grant, Downton Abbey star Michelle Dockery, Sophie Okonedo, nominated for an Oscar for her role in the film Hotel Rwanda, and Olympic swimming gold medallist Adam Peaty.
The service will be broadcast as part of the programme Royal Carols: Together At Christmas, screened on ITV1 and ITVX on Christmas Eve, and will feature three films about the stories of people and organisations who have inspired, counselled and comforted others in their times of need.
She will say: “The Christmas story encourages us to consider the experiences and feelings of others.
“It also reflects our own vulnerabilities and reminds us of the importance of giving and receiving empathy, as well as just how much we need each other in spite of our differences.
“Above all else, it encourages us to turn to love, not fear. The love that we show ourselves and the love we show others. Love that listens with empathy, love that is kind and understanding, love that is forgiving, and love that brings joy and hope.”
