It's been a whirlwind year for Meghan Markle – she left her TV show Suits after seven years, became engaged to and married Prince Harry, announced her pregnancy and completed her first royal tour.
And the Duchess of Sussex couldn't have done it without her most trusted palace adviser: her sister-in-law Catherine.
At the couple's engagement interview, Harry described his brother William's wife as a "fantastic" support to his bride.
"Catherine has been absolutely amazing," the 34-year-old said. And Meghan, 37, agreed, "She's been wonderful."
Now, one year on, sources say that bond has only grown. "Kate is one of the only people who can truly understand what Meghan is going through," a palace source told Woman's Day.
"Harry is very protective of her, but he grew up in this world and she didn't. It's Kate who she can really rely on during her time of need."
It hasn't exactly been smooth sailing for Meghan since she entered the royal family after tying the knot with Harry on May 19. The Duchess has had to weather the storm of several family members speaking about her in the press, as well as facing constant criticism for breaking royal protocol.
"Meghan knew what she was getting herself into, but the level of scrutiny she is under would be tough on anyone," says the insider.
WATCH: Royal confusion! Meghan Markle unsure who gets in the car first. Post continues...
Expectant mum Meghan, who was delighted to announce her pregnancy in Australia, has even faced criticism as she battled morning sickness and nerves during her first major overseas tour.
Some commentators have complained over petty things, like Meghan leaving a tag on her dress and skipping some royal engagements to rest.
"Meghan and Harry loved being Down Under but all the appearances and travelling weren't easy on her, especially with a baby on the way," explains our source. "She's under a lot of pressure at every turn."
However, back at home in England, 36-year-old Kate has been the helping hand the new royal needs.
"Kate is reassuring Meghan that she went through the same thing," tells one palace aide, adding Kate was checking in with Meghan with regular calls while she was on tour.
"Kate has been telling her the most important thing is to look after herself and her baby. She's let Meghan know that none of that other stuff matters."
And while Kate and Meghan are sisters-in-law, they are also fast becoming close friends.
"Kate took Meghan under her wing from the start," adds the source. "They truly are like sisters!"
Kate knows the drill
Just like Meghan, Kate has worked during her three pregnancies, despite suffering from extreme morning sickness before giving birth to her children, George, five, Charlotte, three, and six-month-old Louis.
And she had been married – and a part of the royal family – just over a year when she and William announced she was pregnant with George in late 2012.
"Kate knows what it's like to be under constant watch when she's not feeling her best," a palace aide explains.
"She's always had the full support of the royal family – and now it's her turn to be the supportive one."