The Queen And Senior Royals Attend The Commonwealth Heads Of Government Meeting - Day Three on November 28, 2015 near Valletta, Malta

(L) Prince Charles, Prince of Wales accompanied by Camilla, Duchess of Cornwall take a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta.

Camilla, Duchess of Cornwall walks inside the cathedral as she takes a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta.

(L) Prince Charles, Prince of Wales accompanied by Camilla, Duchess of Cornwall take a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta.

Camilla, Duchess of Cornwall takes a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta. 

Queen Elizabeth II arrives for a visit to Heritage Malta on November 28, 2015 in Kalkara, Malta. Queen Elizabeth II, The Duke of Edinburgh, Prince Charles, Prince of Wales and Camilla, Duchess of Cornwall are in Malta on the final day of a visit to the island that has been hosting the Commonwealth Heads of State Summit.

Queen Elizabeth II attends a prize giving ceremony on a visit to Malta Racing Club at Marsa racecourse on November 28, 2015 near Valletta, Malta. 

Queen Elizabeth II attends a prize giving ceremony on a visit to Malta Racing Club at Marsa racecourse on November 28, 2015 near Valletta, Malta.

 Queen Elizabeth II is greeted by Malta president Marie Louise Coleiro Preca (R) as she arrives for a visit to Malta Racing Club at Marsa racecourse on November 28, 2015 near Valletta, Malta.

Prince Philip, Duke of Edinburgh is shown some rare 17th century Shakespeare books which have been restored at the Kalkara Heritage site on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II and Prince Philip, Duke of Edinburgh embark on a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

 Queen Elizabeth II plants a native Maltese tree in the gardens of San Anton Palace on November 28, 2015 in Valletta, Malta.

Queen Elizabeth II walks in the gardens of San Anton Palace on November 28, 2015 in Valletta, Malta.

Camilla, Duchess of Cornwall takes a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta.

 Prince Charles, Prince of Wales accompanied by Camilla, Duchess of Cornwall pose for a photograph inside the cathedral as they take a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta

Queen Elizabeth II arrives for a visit to Malta Racing Club at Marsa racecourse on November 28, 2015 near Valletta, Malta. 

Queen Elizabeth II disembarks after a tour of the Grand Harbour in a traditional Maltese fishing boat, with the HMS Bulwark amphibious assault ship seen in the background on November 28, 2015 in Valletta, Malta. 

Queen Elizabeth II disembarks after a tour of the Grand Harbour in a traditional Maltese fishing boat, with the HMS Bulwark amphibious assault ship seen in the background on November 28, 2015 in Valletta, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II arrives to embark a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta.

Queen Elizabeth II embarks on a boat for a trip across Valletta Harbour departing from Kalkara and arriving at Customs Wharf on November 28, 2015 in Kalkara, Malta. 

(L) Queen Elizabeth II and President of Malta, Marie-Louise Coleiro Preca visit Marsa racecourse in the outskirts of Valletta on November 28, 2015 in Valletta, Malta.

Queen Elizabeth II arrives to Marsa racecourse in the outskirts of Valletta on November 28, 2015 in Valletta, Malta.

Queen Elizabeth II visits Marsa racecourse in the outskirts of Valletta on November 28, 2015 in Valletta, Malta.

(C) Queen Elizabeth II and Prince Philip, Duke of Edinburgh are greeted by the President of Malta, Marie-Louise Coleiro Preca (L) at San Anton Palace on November 28, 2015 in Valletta, Malta.

Prince Charles, Prince of Wales accompanied by Camilla, Duchess of Cornwall take a walking tour of the old town of Mdina in central Malta on November 28, 2015 near Valletta, Malta.

(R) Queen Elizabeth II inspects the Guard of Honour with the Malta president Marie Louise Coleiro Preca at Luqa airport, before flying home from Malta on November 28, 2015 in Mdina, Malta.

 Queen Elizabeth II inspects the Guard of Honour with the Malta president Marie Louise Coleiro Preca at Luqa airport, before flying home from Malta on November 28, 2015 in Mdina, Malta.

Queen Elizabeth II signs a book as Prince Philip, Duke of Edinburgh (R) looks on at San Anton Palace on November 28, 2015 in Valletta, Malta.

(R) Queen Elizabeth II signs a book next to the President of Malta, Marie-Louise Coleiro Preca at San Anton Palace on November 28, 2015 in Valletta, Malta.