The dancing BBC contestant went to see long-term friend and former neighbour Mandy Bryant, 52, who had battled with breast and liver cancer for four years. During his visit to the Butterfly Hospice in Lincolnshire, he renewed the wedding vows of Mandy and her husband Mick.
She died four days later.
Her son Nathan, 21, told Northamptonshire Telegraph: "Mum and dad wanted to renew their wedding vows next year to mark their 25th wedding anniversary, but after being told their time together was now short, we took steps to bring the occasion forward.
"Richard was only too obliging, having been a family friend for more than 12 years."
The couple became friends with Rev Coles during his time as a curate in the Lincolnshire town of Boston.
Nathan added: "Richard has always been considered a special friend of the family, and we're so grateful for his compassion and support, finding time to come and support the family in our time of need, whilst he's got a full schedule with Strictly and his ministry duties.
"There was a lovely moment when Richard gave us a demonstration of his dance moves in the room for mum. He joked that he had two left feet and needed more practice.
"Surrounded by friends and family he renewed their vows. I'll never forget the smile on mum's and dad's faces."
Rev Coles, who lives with civil partner Rev David Coles, joined the 15th series of Strictly Come Dancing with dance partner Dianne Buswell.
Formerly one half of the 1980s pop band The Communards, Rev Coles is currently a vicar of St Mary the Virgin Church in Finedon near Kettering.