It's the princess's first public appearance since announcing her cancer treatment earlier this year, a show of unity with King Charles, who has also undergone treatment for cancer.

It's been such a challenging time for the royal family, and to have everyone back together on the balcony, I think really reassured people that things are going in the right direction for both the King and for Kate.

Princess Kate also releasing this picture, and sharing a very personal statement Friday, saying she was making good progress, but admitting there are good days and bad days.

On those bad days you feel weak, tired, and you give in to your body resting, adding, on the days I feel well enough, it's a joy to engage with school life, spend personal time on the things that give me energy and positivity.

I think people have seen the princess speaking in a more personal and intimate way than ever before.

She's opened up in a way she never has done before, and sharing her vulnerabilities as well as the positives, you know, in this journey.

The palace sharing these tender moments behind the scenes of Kate with her children, who The family watching dad Prince William on horseback, part of the military pomp and circumstance.

Six-year-old Prince Louis spotted yawning, then dancing, big sister Princess Charlotte giving him a nudge.

The youngest royals all making their social media debut with a touching post on Father's Day, saying, we love you, Papa.

The palace said the picture was taken by Kate.

Prince William posted his own Father's Day tribute to the King.

And Princess Kate said that she was blown away by all the messages of support.

The palace is really stressing that this does not mark a return to full-time duties for the princess.

She herself said in her statement that her treatment is ongoing and will continue for the next few months.

Guys, it's so good to see her.

Kelly, thank you.

Let's talk more about the big weekend and what's next for the royal family.

Katie Nichol is our NBC News special royal correspondent.

She's also Buckingham Palace.

Good to see you, Katie.

Wow.

She looked great.

And we're not 100% sure of how she's actually feeling, but what kind of reaction did she get from the British public?

An amazing reaction.

I mean, often I think some of these events are bigger in America because we kind of get used to this.

We know this pomp and pageantry.

I cannot tell you.

The weather was biblical.

The rain was torrential, but that didn't deter the crowds.

And I think the late night announcement on Friday that the princess was going to attend something we didn't expect.

She'd missed that review of the Irish Guards, of which she is colonel, the week before.

I think that was an indicator, coupled with everything we were hearing from the palace, that she probably wouldn't be up to it.

Well, in fact, she was.

And that appearance up there on the balcony sent a really important message out to the world in a few months that have really rocked the monarchy, with both the king undergoing cancer treatment and the princess of Wales as well.

To that point, Katie, King Charles, as you mentioned, they're also battling cancer.

What did you make of the interaction between the two of them, the king and Princess Kate?

Well, I'll tell you what was interesting about that.

If you flick back to footage from the year before, it was William and his father who were shoulder to shoulder on that balcony.

On Saturday, it was Catherine and her father-in-law.

And they are on a shared journey.

They're part of a club they probably don't want to be part of, but they are.

And I know that behind the scenes, the king has brought great strength to Catherine.

And I was told by a contact very close to her that he's been a pillar of strength.

And I think what was always a close relationship is now even closer.

And how is the king doing, Katie?

So I hear that he's responded to treatment very well behind the scenes.

He's positive.

He's optimistic.

I mean, there were two non-negotiables in his diary, the D-Day landings, which, of course, we saw him both here in the UK and in Normandy, and this, Trooping the Colour.

Both important, both non-negotiable.

And he was here for both of them.

And, of course, today, he'll be at Audra the Garter ceremony.

So I think he's looking well.

But behind the scenes, obviously, it's a challenge.

As Catherine herself said, there are good days and there are bad days.

That's as true for Catherine as it is for the king.

All right, Katie.

Thank you so much.

We appreciate it.

Hey, thanks for watching.

Don't miss the Today Show every weekday at 11 a.m.

Eastern, 8 Pacific, on our streaming channel Today All Day.

To watch, head to today.com slash all day, or click the link right here.