The Prince and Princess of Wales hosted the garden party on behalf of the King, and met guests from a number of both their patronages, military affiliations and passion projects.
Zara Tindall and the Duke and Duchess of Edinburgh also attended the event.
After her meeting with William, Lucas said: “It was like meeting an old friend again, because we had such personal conversations last time we met.”
She said the Prince was “really keen” to know about her campaign but was also “checking in on how I am” and “it was a nice conversation”.
She added: “Today is just magical, it’s a once in a lifetime experience, so I’m really honoured to even be invited let alone get to see them again.”
Of her conversation with Kate, who was wearing a Self Portrait dress and a vintage hat, she said: “Last time I met her I was quite down.
“We met them while the inquiry was going on, so she just said she is so happy to see me full of energy and passion and enthusiasm again.”