Lady Susan Hussey, who resigned as a royal aide following a row over alleged racism, joined the King and Princess Royal for a church service on the royal family's Sandringham estate in Norfolk on Sunday.
Lady Susan, who is Prince William's godmother and was the late Queen's lady in waiting for more than 60 years, looked in good spirits as she arrived at St Mary Magdalene Church.
She stepped down from her role after asking Ngozi Fulani, a black woman who campaigns against domestic violence, where she "really came from" at a Buckingham Palace reception in November.
Lady Susan, 83, apologised after she repeatedly asked Ms Fulani, chief executive of the charity Sistah Space, about her heritage - according to a transcript provided by Ms Fulani, who described the exchange as a "violation".
In comments to The Independent website at the time, Ms Fulani said: "This is bigger than one individual. It's institutional racism ... this incident is unfortunate and shows that nothing has changed."
It happened at a reception held by the Queen Consort to examine violence against women and girls.
A spokesperson for the Prince of Wales described the incident as "really disappointing".
They added: "Obviously, I wasn't there, but racism has no place in our society. The comments were unacceptable, and it is right that the individual has stepped aside with immediate effect."
In December, Lady Susan and Ms Fulanu met again at Buckingham Palace.
Their discussion was "filled with warmth and understanding", the palace said.
"Lady Susan offered her sincere apologies for the comments that were made and the distress they caused to Ms Fulani," it added in a statement.
"Lady Susan has pledged to deepen her awareness of the sensitivities involved and is grateful for the opportunity to learn more about the issues in this area.
"Both Ms Fulani and Lady Susan ... hope that their example shows a path to resolution can be found with kindness, co-operation and the condemnation of discrimination wherever it takes root."
Lady Hussey was married to Marmaduke Hussey, former chairman of the BBC's board of governors.
She accompanied the Queen to Prince Philip's funeral.