The event also commemorated the 100-year anniversary of the World War I.
"The message from the Queen was very much Meghan needed to think about how she speaks to staff members and be careful to follow family protocols", the source added.
Meghan chose a dark navy skirt suit, reminiscent of the pale pink Prada suit she wore to a Buckingham Palace reception earlier in the year.
That meant their wives watched the service from a balcony above, and Meghan was seated in a separate box apart from the senior royals.
The move was reportedly inspired by Harry and William's changing roles, including Prince William one day becoming King. An excellent photo has resurfaced online of Meghan Markle during her pre-Duchess days, which proves that there was another iconic, ginger British guy in her life before Prince Harry was on the scene.
Federal German President His Excellency Frank-Walter Steinmeier laid a wreath on behalf of the German people.
Within the "Top Ten", between Charles and Camilla is where Charles's sister, Princess Anne and her daughter Zara Phillips land.
At 92, Queen Elizabeth is showing no sign of slowing down.
For the second year in a row, the Queen, 92, handed her duties over to her son and heir to the throne, the Prince of Wales.
But royal fashion aficionados were quick to point out a mysterious splatter on her right foot and leg.