Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1936 Marlborough House became the London residence of the queen dowager , Mary of Teck , widow of King George V. Following Queen Mary 's death in 1953 Queen Elizabeth II donated it for use by the Commonwealth Secretariat , which continues to use it today .
Simplified: It continued as a royal residence , and was last used by Queen Mary until 1953 . After her death , her granddaughter , Queen Elizabeth II , gave the house to the Commonwealth Secretariat , which continues to use it today .