The princess has “smoothed the way for William and his father to have a better relationship than they had in the past,” author Robert Jobson writes

King Charles, Kate Middleton and Prince William. PHOTO: YUI MOK/POOL/AFP VIA GETTY IMAGES; CHRIS JACKSON/GETTY IMAGES; CHRIS JACKSON/GETTY IMAGES

Kate Middleton’s soothing effect on Prince William has helped him improve his relationship with his father King Charles, according to a new book.

An excerpt of Robert Jobson’s upcoming biography Catherine, The Princess of Wales obtained by The Daily Mail details how the Princess of Wales, 42, has been a “calming influence” on the whole royal family — especially William, 42.

Through her role as an “instinctive peace-maker,” Kate has “smoothed the way for William and his father to have a better relationship than they had in the past,” Jobson writes.

King Charles and Prince William in 2024.MAX MUMBY/INDIGO/GETTY

A senior source in Catherine echoed this. “In recent years, they have become much closer,” the insider said of the King’s relationship with his eldest son.

“He also respects his father and his devotion to service, but he feels the fact his father put work first had a detrimental impact on him when he was growing up and didn’t help their father/son relationship,” the source added.

Still, an insider told Jobson that Kate has helped William see his father’s perspective. “[She] is somebody who always tries to see both sides of any dispute,” they said, adding that the “emotionally mature” princess “is a stabilizing influence.”

Her positive influence also extends to the King, who views her as his “beloved daughter-in-law” and even the daughter he never had, Jobson writes. Kate, meanwhile, privately addresses him as “Grandpa,” the book claims.

King Charles and Kate Middleton.SAMIR HUSSEIN/WIREIMAGE; MAX MUMBY/INDIGO/GETTY

Jobson also claims the monarch is always excited to see the princess, heading her way immediately when he spots her at family events. He usually greets her with a “loving kiss,” and the pair is “often seen laughing and joking together,” the author writes.

Elaborating further on the pair’s relationship, a courtier told Jobson, “I think the [King] understands Catherine is a good influence on the entire family.”

“He loves and truly appreciates everything she does,” the courtier added.

When it comes to Kate’s calming influence, the Prince of Wales has returned the favor in many ways. As she undergoes treatment for her treatment for cancer, which she announced in March, the prince has been by her side.

“Having William by my side is a great source of comfort and reassurance too,” Kate said while announcing her condition in a video message. “As is the love, support and kindness that has been shown by so many of you. It means so much to us both.”

Prince William and Kate Middleton in 2024.

Similarly, as King Charles also undergoes treatment for his own cancer, he is “so proud of Catherine for her courage in speaking as she did,” a Buckingham Palace spokesperson told PEOPLE in March.

Both the monarch and princess were hospitalized at The London Clinic in January, and the King has “remained in the closest contact with his beloved daughter-in-law throughout the past weeks,” the spokesperson added at the time.

Catherine, The Princess of Wales will be available to purchase wherever books are sold on Aug. 6.