The Prince of Wales will highlight the shared goals and enduring bonds between Barbados and the UK during a ceremony marking the Caribbean country's transition to a republic.
Charles will also tell the nation it is "important" for him to attend the event, being staged in the capital Bridgetown, to "reaffirm those things which do not change" as the major constitutional shift takes place.
The heir to the throne will deliver his address just after midnight as Barbados begins a new chapter in its history on Tuesday - the 55th anniversary of independence from Britain - after its first president Dame Sandra Mason is sworn in.
Barbados' decision to remove the Queen as head of state will be watched closely by other members of the Commonwealth especially in the Caribbean region.
During the ceremony in National Heroes Square, Charles is expected to say: "As your constitutional status changes, it was important to me that I should join you to reaffirm those things which do not change."
He will go on to give examples of the ties that will remain - "the close and trusted partnership between Barbados and the United Kingdom as vital members of the Commonwealth" and "our common determination to defend the values we both cherish and to pursue the goals we share".
Charles is also expected to celebrate the cultural, social and economic bonds between the UK and Barbados, "the myriad connections between the people of our countries - through which flow admiration and affection, co-operation and opportunity - strengthening and enriching us all".
Barbados is following other Caribbean nations that have dispensed with the Queen as their head of state, with Guyana becoming a republic in 1970, Trinidad and Tobago following in 1976 and Dominica two years later.
Jamaica has also flagged it wants an elected head of state.
The Queen has been Barbados's head of state since it became independent in 1966 but the issue of becoming a republic has been discussed for decades.
Barbados is one of the Queen's 16 realms - countries where she is head of state - and in the Caribbean region other countries include Antigua and Barbuda, Bahamas, Belize, Grenada, Jamaica, Saint Kitts and Nevis, Saint Lucia and St Vincent.
Australian Associated Press