Kate Middleton's 'Immaculate' Appearance: Princess of Wales Receiving Extra Care During Cancer Battle

Kate Middleton dazzled at Trooping the Colour on Saturday, June 15, but the Princess of Wales' return to the spotlight wasn't easy. Kate took a step back from duties to focus on her health after being diagnosed with cancer, but the mom-of-three managed to attend the gathering.

"The princess has this sort of swan-like quality about her — she's sort of gliding on the surface — but beneath the water, I think often she's paddling quite frantically," Katie Nicholl told an outlet. "I can only imagine that a huge amount of preparation and time and effort and energy will have gone into Saturday's appearance."

Kate Middleton's "immaculate" appearance was praised by Nicholl.

"She was on her feet for a long period of time," Nicholl continued. "There was a moment where she was watching the parade... and was offered a seat, which she gratefully accepted. That's just a bit of an acknowledgment that she is not as strong, not as fit, as she was before she went into this treatment."

Kate is focused on her recovery, but she shared in an Instagram post that she sometimes feels "weak and tired" while undergoing chemotherapy.

"I think a day like Saturday, where she knows the eyes of the world are on her, there is a huge amount of scrutiny that will take its toll," the author noted. "I think we can probably imagine that she probably had a long and well-deserved rest afterward. I don't think we can expect to see her in public for a little while. That's going to take some recovery from."

Although fans were excited to see Kate in attendance, the princess isn't being rushed to get back to work.

"There was no pressure on her from anyone. She really wanted to do this," Nicholl said. "She turned a corner in her treatment... When she turned that corner, I was told that Trooping was a goal for her. She was given the sign-off by her medical team. She spoke to her father-in-law about attending and to Prince William. They were fully behind her."

"Charles has been a great pillar of support to Catherine when she said that she'd really like to be there at Trooping," she added. "He was 100 percent behind it. The idea that she was going to upstage him didn't even cross his mind. He just wanted his daughter-in-law by his side."

While waving at fans, Kate was able to be a calming figure for her three kids, Prince George, Princess Charlotte and Prince Louis.

"I think she felt very much that she needed to be there," Nicholl claimed. "The children looked so happy and relaxed having their mother there... It was important, I think, for the Princess of Wales to be there to support her father-in-law, to be there for her family, and to be there for the nation to send out a really important message that she's doing OK."

Nicholl spoke to Entertainment Tonight.