A portrait of King Edward.

A hidden painting of Queen Elizabeth I and an 18th century insect have been uncovered by art experts preparing an exhibition of royal portraits.

The portrait of the Queen was painted over sometime in the 18th century to make her appear more modern and only revealed when it was X-rayed ahead of a show at the National Portrait Gallery.

The gallery’s chief curator Tarnya Cooper said: “Elizabethan portraits were rarely appreciated as art objects in later centuries, but Elizabeth’s reputation as a Protestant champion meant that there was still demand for her image.

“As a result, artists often reworked original portraits into images that adhered to contemporary notions of beauty.”

The beetle was found when experts examined a portrait of King Edward VI and is thought to have been trapped when it was varnished several hundred years ago.

Other works on show include a plaster and wood bust of King Henry VII, which was originally part of a life-size effigy of the king made for his funeral procession, and six portraits of King Henry VIII.

Cooper said the show was the result of “seven years” of work, adding: “Visitors will encounter multiple lifetime portraits of each monarch, providing a fascinating and vivid impression of one of the most dynamic dynasties in history.”

• The Real Tudors: Kings And Queens Rediscovered runs at the National Portrait Gallery in central London until March 2015.