Kate Middleton and Prince William have been lovebirds for over 20 years — enduring marriage, children and palace life together.

Royal expert Jennie Bond said their bond is so strong because the Duchess of Cambridge, 41, gives William, 41, what he “was lacking in his own family life.”

Bond told OK! magazine that the pair’s strong relationship is a sharp contrast to the one the Prince of Wales had with his father King Charles and his mother, the late Princess Diana.

“[Middleton has] given William everything he didn’t have with Charles and Diana,” the BBC correspondent said.

She added that Middleton has provided William with a “loving, deep partnership, founded on friendship, passion and mutual respect, plus a broader, settled and happy relationship with his in-laws.”

The couple married in April 2011 at Westminster Abbey, but have known each other since 2001.

When they tied the knot, William gained mother-in-law, Carole, and father-in-law, Michael Middleton.

According to Bond, they “welcomed William into their home and treated him like one of the family. He can relax with them, trust them, and be himself in a way he can do with only a very few others.”

William and the mother of three have now known each other longer than he has lived with Diana — who died in 1997 when he was 15 years old.

However, William shares much of his mother’s same devotion to charitable causes like eradicating homelessness.

His mother’s influence is still prevalent in the way he carries himself in public.

Bond explained: “It was, of course, Diana, who first showed her sons the plight of homeless people. Now, William has said that he wants his own children to be fully aware of how privileged they are and how other people may sometimes need a little help.”

“Then there is Catherine’s influence,” Bond noted. “She has won not only his deep love but his respect.”

While Charles, 74, became a single parent to William and his younger brother, Prince Harry, after Diana’s death, the monarch was more removed as a father and didn’t spend as much time with his sons when they were kids.

As time went on, Charles has become “closer” with William, however, Bond believes that it’s “the women in his life who have helped make him the man he is.”

“His grandmother, the late Queen [Elizabeth], was there for him — as he said — through the happiest and saddest times of his life,” the expert said.