Prince Charles on the moment William moved him to tears

Prince Charles has shared a special moment when Prince William reduced him to tears.

In the ITV docu-series Prince Charles: Inside the Duchy of Cornwall, royal fans are offered a rare look into the Prince of Wales's life.

The series follows Charles, 70, carrying out his royal duties but also highlights his relationship with sons Prince William, 37, and Prince Harry, 35.

In a new episode airing in the UK today, William, who is second in line to the British throne and first in line to inherit the Duchy of Cornwall from Charles, meets with tenants of the private estate.

After hearing a conversation that William had with Mervyn Keeling, a second-generation Cornwall tenant, Prince Charles says he was overcome with emotion.

"I saw it and I couldn't believe it. I was deeply touched by what he said," Charles said in a clip from the episode, released by ITV.

The conversation between William and Keeling was about the significance of family in the process of succession.

"I think it's important, Mervyn, about the family angle. I really do," the Duke of Cambridge says in the clip. "I've started to think about how I will inherit the Duchy one day and what I do."

Prince Charles is currently the Prince of Wales and the Duke of Cornwall, which means he oversees the Duchy of Cornwall estate. When he eventually becomes King, Prince William will take over both the titles and the role.

William added that having children (Prince George, six, Princess Charlotte, four and Prince Louis, one) has changed how he things about the future role.

"Frankly, it reduced me to tears. It did really, because I suddenly thought, well, just hearing that from him has made all the last 50 years worthwhile."