"I think it's fantastic that the royal family now has a beautiful biracial bride. Who would have thought it? I never thought I would live to see that, and I'm so glad to see it."

But she added: "It's much more difficult these days to keep a relationship going - and it's because of the internet. It gives people unreasonable expectations, like that a Prince Charming will come riding in on a horse.

"Meghan is lucky, a Prince Charming did walk into her life, but I'm very concerned about those who are lonely."

The 4ft 7in sex (1.4 metre) therapist said that addiction to social media meant "loneliness" was going to become a bigger problem than "sexual literacy", which she used to guide the nation on.

"I'm very concerned about loneliness," she said. "People are losing the art of conversation. They're constantly on their iPhones.

"You see the couples sit down in restaurants both with their phone on the table. It's a big problem for the relationships."

To that end Dr Ruth is planning a return to television with a programme aimed at millennials. She will have a young, male co-host and has promised to do her best to let him get a word in.

"What the young people need now is a voice like mine, a little bit old fashioned and square," she said. "We need to tell them to put the phone aside, and put their energy into forming relationships. You can't ignore the phone, that's the way we live now, but you have to know not to be addicted."

Dr Ruth became an iconic figure in the Eighties when she was already in her 50s, with her books, TV and radio appearances during which she dispatched unprecedented bedroom advice to Americans, matter-of-factly using words that had previously been too shocking for mainstream broadcasts.

The German-born dynamo shows no signs of slowing down. She has two books out, including a new graphic novel-style autobiography called Roller-Coaster Grandma.

It details her extraordinary life which began as an orphan of the Holocaust, escaping from the Nazis as a child on a Kindertransport. She went on to train as a sniper with a Jewish paramilitary group, then emigrated to the US where she went from being a maid to a professor, and eventually a sex therapist.

This week she celebrated her 90th birthday at the Museum of Jewish Heritage in New York where, as ever, she was interested in the sex lives of her 350 guests. "It was just a fantastic, wonderful birthday" she said. "Please tell the Queen I will be waiting for the telegram when I'm 100."

Telegraph, London