Kate's husband Prince William is away and busy with his work as an RAF search-and-rescue pilot, so she has been using her free time to give Harry some domestic tips, reported Femalefirst online.
"Kate is a whizz in the kitchen, while Harry's skills are rather lacking. So Kate has been teaching Harry to cook rather than use the microwave," said a source.
"They have a very brotherly, sisterly relationship and Harry has been a great support to Kate, who is still fairly new to the royal family," the source added.
Harry along with Kate have jokingly nicknamed William "Burger King" after he gained a few pounds recently.
"It's always a laugh when Kate and Harry are together. William loves that his wife and brother are such good pals and he jokingly calls Harry, Kate's 'lady in waiting' because he's always there by her side. What he doesn't enjoy is how much they like to wind him up," the source said.