"Everyone was disappointed that they did not get to catch up with Meghan given everything that has happened to her," a former friend told MailOnline, adding the letter was addressed to the reunion class of 1999 from Kensington Palace.
"But the whole group was super excited about her giving birth to the first British-American prince, it was all anyone talked about."
The pal continued: "They were so excited to get that letter from her. She is remembered as someone who is very thoughtful, and to get that kind of attention now that she is a Royal went down really well.
"Hopefully she will be able to make it to the 25 year reunion and she is welcome to bring Harry and Archie along with her."
A total of 37 of Meghan's former schoolmates from Immaculate Heart High School attended the reunion on May 5.
The Duchess gave birth to her first child the following day.