Kate wore a new Alexander McQueen coat dress for today’s garden party at Buckingham Palace.
In this video from Rebecca English, you can see Kate, William, HM, and other royals as they arrive and the national anthem is played.
And the National Anthem….. pic.twitter.com/TsIwhZC4dq
— Rebecca English (@RE_DailyMail) May 21, 2019
The Duke, Duchess, and HM as the national anthem is played. 
Another view.
There are usually about 8000 guests at the Buckingham Palace garden parties. The functions are considered a good way for HM to meet and speak with a wide cross-section of people, all of them selected because of the positive impact they have made in their community.
Below, you can see the “lanes” guests are standing in; royal family members will take a given lane and greet the guests.
Kate and William with guests.
More about the parties from a story in The Express:
The Queen will welcome more than 30,000 to the grounds of Buckingham Palace and the Palace of Holyroodhouse this summer.
Around 27,000 cups of tea, 20,000 sandwiches and 20,000 slices of cake are consumed at royal garden parties every year.
HM with I-don’t-know-how-many camera phones aimed at her. (I always thought taking photos of the royals wasn’t allowed at these functions, but I could be wrong about that.)
More about the events from the Royal Family site:
…a long established network of sponsors is used to invite guests, who include Lord-Lieutenants, Societies and Associations, Government Departments, Local Government, the Services, the Church and other Faiths. They nominate guests for invitation and we hope in this way to achieve a representative cross section of the community.
Here you see HM meeting artist Yinka Shonibare.
More about the artist from Art21.com: “Known for using batik in costumed dioramas that explore race and colonialism, Yinka Shonibare CBE also employs painting, sculpture, photography, and film in work that disrupts and challenges our notions of cultural identity.”
Below you see the artist receiving his CBE from Prince William earlier this year. 
All members of the Royal Family attending the event greet additional guests.
Below, the Duke of Kent.
The Duke of Gloucester is seen in this photo.
Below, Princess Alexandra with attendees. 
Sophie, Countess of Wessex. (I believe she is repeating an Emilia Wickstead design.) 
Prince Edward. 
And Prince Andrew. 
In this photo, you can see a staff member giving Kate and William names/quick background info on the guests they are meeting.
Rebecca English tweeted a quick video of Kate and William.
— Rebecca English (@RE_DailyMail) May 21, 2019
Another view of the Duke and Duchess. 
The couple had quite the laugh at one point. 
There were several additional photos posted on Instagram by Kensington Palace. You can see them here by just clicking on the image below.
Now for what was worn at Buckingham Palace today. The Queen wore a dress/coat combination from royal favorite Stewart Parvin, with a hat by Rachel Trevor Morgan.
The Duchess was in a new Alexander McQueen design. 
The coat dress has many of the design elements Kate is fond of, especially in McQueen garments. The piece is double-breasted, with a very slightly raised shoulder, pleats at the front and back, as well as a partial peplum. UPDATE: For no reason that I can think of, temporary insanity reigned as I wrote the post and I used the phrase “partial peplum,” when it clearly doesn’t have a peplum of any kind. Thank you to Chelle for her comment pointing this out. 
The bodice is somewhat similar to the Samurai Coat by the brand Kate has worn, although the buttons on today’s garment are closer than those on the Samurai Coat.
Below left you see the peplum on the left front of the garment; on the right, the peplum across the back.
Kate’s hat was by Juliette Botterill.
She carried her Loeffler Randall clutch and brought back her Gianvito Rossi suede pumps in the praline colorway. 
The Duchess wore the Collingwood diamond and pearl drop earrings that belonged to Diana, Princess of Wales. 
We’ll leave this portion of the post with a Royal Family Channel 3-minute+ video from the party.
++++++++++++++++++++++++++++++++++++++++++++++
One other quick note today: the trailer for the Downton Abbey film has been released.
Parveen
Thursday 3rd of November 2022
Elegant and the color suits her. The complete outfit is beautiful.
TwinMamaPlus1inMN
Wednesday 29th of May 2019
I don't love it. It's in her wheelhouse for sure and it's basically part of her "uniform" that she has adopted over time. It works for her for the most part, but isn't interesting or unique. Just another pretty pink coatdress in a sea of many.
Her hair, makeup, and earrings are fab, and her smile and warmth when chatting with people show she is happy and at ease. Those things outweigh my quibbles with her sartorial choices at this event.
Lovemyson12
Saturday 25th of May 2019
I am not a fan of this outfit as much as her others. I do not like the hat at all, it looks much, much too bulky and big for her style. I can barely see her face in it. I like the coat dress but I always like her in those. I guess the pink seems appropriate given its a garden event. I dont know, is it me, or do others not like the hat? It was the first thing that popped out, and believe me I loooove the duchess and her clothing choices!
myra
Sunday 26th of May 2019
love, love the hat. So on trend for many stylish race meetings that are happening around the world. Kate is really adopting a signature look for the more formal events.
Crystal
Saturday 25th of May 2019
If I recall correctly, she’s worn hats much larger than this one and a good portion of others that she’s worn are about the same size as this one. I can see most of her face, except for the part of her forehead it’s tipped down over... maybe the angle and degree its tipped down at are throwing you off? As it does obscure a bit of her face for that reason. Personally I love this hat because it’s so feminine and romantic. But I know what I see as feminine and romantic others will see as fussy and overdone. Personal perspective! It’s the beauty of fashion :)
Shannon
Friday 24th of May 2019
It's so cute and so kate and the twee pink really goes with the softness of the queen's outfit.A tad disappointed by the clutch though!
Lindsay
Saturday 1st of June 2019
I do love the pink color and I think her hat and jewelry is fabulous. I honestly want to know what is in the clutch… it looks like it is empty! I think I always preferred her more structured clutch bags (does anyone else miss the LK Bennett Natalie?).
She and William are so cute together. I just watched the documentary that was made in honor of their one year anniversary. Cool footage that I’d never seen before!
Jane
Friday 24th of May 2019
Kate just looks more and more regal at formal events. She looked impeccable today and like the future queen. I thought the color and tailoring on the dress were so gorgeous with this beautiful hat. I also loved that William had a pale pink flower on his lapel. Such a perfect subtle way to coordinate with her. He looked so handsome.