Biden, 81, says the key to his marriage is 'good sex': How Joe infuriates Jill, his wife of 47 years, with VERY risqué joke to staff about their private life (even though they aren't shy about PDA)

Even after 47 years of marriage, the romance between President Joe Biden and Jill Biden is far from dead. 

From kisses before he boards Air Force One to date nights and him introducing himself as 'Jill's husband', the stress of the White House has showed no signs of straining their relationship.

But, in private, the president has revealed some very risqué secrets about why their bond is so strong, much to his wife's annoyance.

He infuriates wife Jill by joking that the key to their 47-year marriage is 'good sex'.

His racy comment has been revealed for the first time by Katie Rogers in her forthcoming book 'American Woman: The Transformation of the Modern First Lady, from Hillary Clinton to Jill Biden,' in an exclusive excerpt obtained by DailyMail.com.

The president gives that marital advice to aides 'much to his wife's chagrin,' reports Rogers, a longtime White House reporter for the New York Times.

President Joe Biden, who has been married to Jill Biden for 47 years, says the key to a long and happy marriage is 'good sex'

Biden has long spoke of his love and devotion to his wife, saying it's more important to him than anything else.

'I'd rather be at home making love to my wife while my children are asleep,' he said in 2006 when asked about running for the Democratic nomination in the next presidential election. Two years later he ultimately did make a run and lost to Barack Obama, taking the number two spot on that ticket instead.

His spokesman at the time said Biden's comment illustrates that a White House bid 'is not an egotistical pursuit for him' and that he is, 'frankly, totally in love with his wife.'

Rogers' book, out Tuesday, shines a spotlight on modern first ladies as two of them - Jill Biden and Melania Trump - wait to see if their husbands' quest for a second term in the White House succeeds. 

The book examines the evolution of the unpaid role from when Hillary Clinton held it to the current East Wing ran by Jill Biden, from how each woman shaped the position and how it is tied to the holder's husband. 

The Bidens are an openly affection couple, showing their love for one another with public romantic gestures.

The president took his wife out for a date night in Rehoboth Beach in August, where the couple had a seafood meal at Matt's Fish Camp and then headed to the local theater to see Oppenheimer, the film about the man who developed the atomic bomb.

They concluded their date night with a romantic walk on the beach to see the super moon, which is when a full moon occurs near the Moon’s closest point to Earth in its monthly orbit. The president had his arm around the first lady.

There have been other moments. 

Biden stopped to pluck a dandelion from the grassy ground for his wife in April 2021 as the couple prepared to board Marine One for a trip to Georgia. The couple has exchanged kisses in the Oval Office and out in the open as they prepare to part for work trips.

President Joe Biden kisses first lady Jill Biden in the Oval Office; American Woman by Katie Rogers examines the Bidens' relationship

Joe Biden campaigning for president in 1987 with wife Jill and children (from left) Hunter, Beau and Ashley

Jill Biden often stands on the Truman Balcony, watching the president come home from trips

First lady Jill Biden (left) and President Joe Biden (right) in front of her White House's Valentine's Day decorations 

President Joe Biden and First Lady Jill Biden are silhouetted by motorcade lights as they walk on the beach to see the super moon during their August date night in Rehoboth Beach

President Joe Biden stopped to pick a flower for wife Jill as the couple prepared to board Marine One ahead of their trip to Georgia in April 2021

For her part, Jill Biden places cardboard hearts on the North Lawn of the White House for Valentine's Day, calling it one of her favorite holidays.

She also has been seen frequently on the Truman balcony, waiting for Biden to return from a trip, watching him walk from Marine One to the White House.

'One thing in my life has stayed the same: Joe and I have always had each other,' Jill Biden wrote in her memoir Where the Light Enters.

The first lady, in particular, paints the president as a romantic, showing his emotional empathy when she talks to donors and supporters of their campaign. 

She often recounts Joe's courtship of her after his first wife and daughter died in a car crash in 1972. She tells how he had to propose five times for her to say yes because she wanted to be sure it was forever so young Beau and Hunter Biden wouldn't experience loss again.

'I really felt that this marriage had to work. Because they had lost their mom, and I couldn't have them lose another mother,' she has said. 

The Bidens married in 1977 - even taking the boys on their honeymoon - and, in 1981, they welcomed daughter Ashley together. 

Rogers, in her book, examines the evolving relationship between the Bidens as Joe repeatedly ran for president before finally winning the office in the 2020 election.

She also reveals how Jill Biden became her husband's top adviser after their son Beau died in 2015, 'taking more of a role in her husband's political decision-making than she had before.'

'Beau's death changed the family,' Rogers writes.

'Joe was without one of his closest advisers, whom he often described as "me, without all the downsides." Without their older brother, Hunter was in shambles and Ashley, who has also struggled with addiction, was bereft. Once again, it fell to Jill to hold her family together. Instead of calling Beau several times a day to check in or run decisions by him, Joe began relying on Jill more than ever,' Rogers notes.

'She's one of the few people that can really tell him what's up,' a close friend of the couple said.

Even as she focuses on her career outside of politics - teaching English at Northern Virginia Community College - Jill Biden has been a force in her husband's political ascent and will be a key player in this year's re-elect effort. 

She travels the country often to brag about his policy initiatives and to defend his tenure in the White House.

She proved herself a prolific fundraiser for Democrats in the 2022 midterm election and has harnessed that power to help fill Joe Biden's campaign coffers ahead of this year's presidential contest.

And she also keeps the famously tardy president on time, gently tugging at his arm or elbow when he lingers too long talking to supporters or doing interviews with the press. 

President Joe Biden and first lady Jill Biden kiss on the South Lawn of the White House after arriving on Marine One

Jill Biden with Beau Biden, who served in the Delaware National Guard

President Joe Biden, first lady Jill Biden, Hunter Biden and Baby Beau Biden on the Truman Balcony on July 4th

Joe Biden (center) and Jill Biden (right) arrive with family for a Beau Biden's funeral mass on June 6, 2015 with Beau's widow Hallie and his children little Hunter and Natalie, behind them walk Hunter Biden and his eldest daughter Naomi

In their personal life, both Bidens are both fierce protectors of each other and their family.

It is clear Joe Biden loves his wife. He often introduces himself as 'Jill Biden's husband' and says to her: 'Jilly, you're the love of my life and the life of my love.'

For her part, the first lady is a protective defender of her husband to the point where she would physically confront protesters on the campaign trail during the 2020 contest. 

In the White House, she is known as 'one who is not to be crossed.' 

And she is involved with the West Wing, sitting in when the president interviews people for senior staff positions.

'She is present for every major political discussion involving her husband and sits in during the interview process on most major Biden staff hires, from cabinet secretaries to spokespeople. Sometimes, she gets her own separate audience with a new hire,' Rogers writes. 

And Jill Biden is known to question the president's senior aides when she thinks he's not being served.  

When President Biden participated in an over two-hour press conference in 2022, where he made some gaffes, she demanded to know who was responsible for letting the questioning go on and on and on.

She entered a senior staff meeting in the West Wing and demanded: 'Why didn't anyone stop that?' 

And both Bidens are protective of their family, particularly son Hunter, who has struggled with a drug and alcohol addiction.

When Joe Biden was weighing a third White House bid in the runup to the 2020 election, his advisers warned the couple there would be intense scrutiny focused on the children and grandchildren, particularly on Hunter.

'The Bidens were privately told that struggles within their family, including Hunter's ongoing battle with substance abuse, which was not widely known at the time, might bleed over into' the campaign, Rogers writes.

The issue is so sensitive with the couple that only senior staff - most of whom are advisers dating back to Biden's time in the Senate - dare discuss the matter.  

Biden's devotion to his son 'had left him unwilling to take 'an accounting of the vulnerabilities in his life,'' a source close to the family told Rogers. 

Other Biden allies revealed the overarching fear that 'Hunter's sobriety and mental health are so precarious that saying or doing the wrong thing could result in Joe losing his last surviving son.'

Currently, Hunter's business dealings are under investigation from Congress. Republicans charge that Joe Biden benefited financially from Hunter, who used his father's political position to cultivate business practices. The president has said repeatedly he has had nothing to do with Hunter's business dealings.

But Hunter has become a political issue for the president's re-election campaign as Republicans hammer at him, allegedly corruption on the part of the Biden family. The president has been clear in his support for his son.

Jill Biden has defended Hunter repeatedly and publicly. 'I know that Hunter is innocent. I love my son, and I will keep looking forward,' she told NBC News in 2022.

She also makes sure Hunter and his wife Melissa Cohen are welcome at the White House. The couple has attended two state dinners, including one for the Indian prime minister that took place shortly after Hunter made a sweet heart deal to keep himself out of jail.

Attorney General Merrick Garland was also in attendance at the dinner and carefully stayed across the room. The deal later fell apart under scrutiny from a judge.

Jill Biden kisses grandson Beau Biden as his parents Hunter Biden and Melissa Cohen look on during a December 2021 event at the White House

President Joe Biden hugs son Hunter during a visit to Los Angeles earlier this month

Hunter and his family, including his young, photogenic son Beau, are also seen at holiday events like the White House Easter Egg Roll and the arrival of the White House Christmas Tree. Hunter's clan is regularly with the president and first lady when they go to Nantucket for Thanksgiving. 

Jill Biden told Rogers in an interview for the book: 'I'm his mom. I mean, I have to support him and love him, and, you know, I'm constantly talking to him, sending him texts: 'How you doing?' Because it's tough. They've already really been hard on him.'

But the most important role Jill Biden may play is one she has taken on for herself, one that goes outside the office of first lady: the 'family's self-appointed grudge holder.'

'She's an Italian,' one friend said of her. 'She's all about loyalty.'