President Joe Biden joked to his partners that the “key” to a long-lasting marriage was “good sex,” according to a new book about first lady Jill Biden that sheds light on their 47-year romance.

The book “American Woman – The Transformation of the Modern First Lady, from Hillary Clinton to Jill Biden”, written by New York Times White House Correspondent Katie Rogers. The piece about sex is only a few paragraphs long, but it has already made headlines, according to Reuters.

The reporter writes that Biden chose not to run for president in 2004, a decision highlighted to aides when Jill Biden entered the room wearing a T-shirt with the word “NO” emblazoned across her stomach.

Joe Biden, now 81, told a group of supporters that year that he had no particular interest in running for president. “I’d rather be at home making love to my wife while my kids sleep,” he said.

“Joe Biden may have limited his public remarks about the ‘bedroom’ (during his presidential victory), but he has joked with aides that ‘good sex’ is the key to a happy marriage, to much to his wife’s dismay”according to the journalist and author of the book.

The book describes the anguish experienced by Joe Biden when his first wife died in a car accident in 1972 along with their daughter Naomi. He and Jill married in 1977, but it took five proposals from Biden for Jill to agree.