Dr. Ruth Westheimer is the world’s most famous sex therapists. She has written over forty books and she has met world leaders like Princess Diana and Barack Obama, but she is very clear about what her greatest accomplishment is.

“It was wonderful,” she said, “to teach the British about orgasms!”

With her television show “Good Sex!,” Dr. Ruth revolutionized the way people talked about sex.

“And I loved coming to England,” she said. “It made me smile to think of the British with their umbrellas and top hats being in bed.”

Though Dr. Ruth is 91, she is not slowing down anytime soon. She just finished a new edition of her best-selling book, “Sex For Dummies.” Earlier in the summer, Dr. Ruth took part in a Oxford Union debate on pornography, “and just last night I was [in a hotel] and plenty of young people recognised me. At the age of 91 and a half — you must say the half — that makes me very happy.”

Born in Germany in 1928, Dr. Ruth lost both her parents in the Holocaust. After spending the war in a Swiss orphanage, Dr. Ruth moved to New York and was well into her 50s by the time her career as a sex therapist took off. Now, a new documentary called Ask Dr. Ruth is telling her incredible life story.

“I have an obligation to live large and make a dent in this world,” she says in the movie.

Dr. Ruth said that she met Princess Diana two years before her death, “and I thought she was wonderful. I thought her contribution to mankind was in how humane she was.”

When asked if Diana asked her for advice, Dr. Ruth replied, “No, she did not, but I can tell you if she would have asked me for advice, you would not have known about it!”

“I never ever would have talked about it. But, of course, famous people did ask me for help. They were like anybody else and they would often tell me their problems because they knew I knew what I was talking about and wasn’t just a celebrity talking off the top of my head,” she said. “I was also fortunate because my office was not in a fancy part of the city and was in a building where there were many doctors, so no one would know who they were going in to see.”

Dr. Ruth also has advice for older people when it comes to their sex lives.

“No sex in the evening when they’re tired,” she said. “The best way for older people to engage in sex is after a good night’s sleep.”

Check out the trailer for Ask Dr. Ruth below!