Ritchie sings Diana song to William
Lionel Ritchie performed his 1984 hit Hello for the Duke of Cambridge at a charity event tonight, telling the audience it was the favourite song of William's mother, Diana.
The US soul singer dedicated the song to the Duke as he performed at Alexandra Palace in north London.
Sitting at a piano on stage, Ritchie, 65, said: "Many years ago I had the pleasure of meeting Princess Diana and tonight we have Prince William here.
"I must tell you it is a pleasure to be with all of you but especially this gentleman, because his mother came to me ... and she said 'My favourite song is Hello'.
"So I thought tonight the dedication is to you, my friend."
The event was a special dinner to celebrate the 25th anniversary of a charity which provides health and social care support to the UK's Jewish community.
William began his speech at the Jewish Care event by joking that the 1,400 guests would give Ritchie a harder time than the crowd at the Glastonbury festival, where he will perform later this month.
He quipped: "I imagine this crowd is a lot rowdier than what you will have at Glastonbury."
Ritchie met William prior to going on stage and reminded him that he gave him and Prince Harry their first ever music tour jackets at a concert in the 1980s.
The singer said: "His mother and I were very close friends.
"I'm very proud of him as a father. I congratulated him on that.
"Back on my All Night Long/Dancing On The Ceiling tour I gave them - he and his brother - their first tour jackets.
"The joke with that was how long will they be able to wear them and I said 'Not long'.
"(Tonight) I said 'Of course you're six feet whatever now, way out of those jackets'."
He went on to explain the importance of the work done by Jewish Care to look after elderly people, and recalled how he cared for his own parents.
"They raised me and then it was my time to take care of them," he said.
"And by the way, if we go back and talk to (the elderly), they actually have more wisdom than we have now today.
"They have been the pillars of our community for many years and to not take care of them and not pay attention to them is a travesty."
It is the first time William has attended an event for the British Jewish community.
Jewish Care was created through the merger of two charities in 1990.
The Duke told the audience of the organisation's clients, staff, volunteers and supporters: "The results of your commitment to one another within the Jewish community are obvious - the real and loving care that thousands of elderly and vulnerable people receive, among the many works that you carry out.
"Your care for one another has another, less tangible value.
"During a year when many in the Jewish community have had cause to feel under threat, for no reason other than simply the fact of your Jewishness, your unity is all the more precious.
"Your commitment and loyalty to one another, and to society more widely, is ultimately what keeps you strong."
He added: "Through your generosity and commitment, I am sure Jewish Care will continue to thrive and grow for the next 25 years.
"Once again, congratulations on everything you have achieved. I wish you a wonderful evening and a happy birthday. Mazel tov."
Jewish Care has 1,500 staff and 3,000 volunteers.
The organisation provides social and recreational programmes for people of all ages.
Its youth leadership scheme gives young people the opportunity to develop their leadership skills while volunteering in the community.