The former king of Romania is due to address parliament in Bucharest for the first time since he was forced to abdicate in 1947.
King Michael I - who will reportedly be sitting on a special throne-like chair - will be speaking ahead of ceremonies marking his 90th birthday.
Members of Europe's royal families will join him at a gala concert at the Romanian Opera before a private dinner.
But officials say there are no plans for Romania to revert to a monarchy.
"We want to honour and to celebrate an important person of our history and of contemporary history," Romania's Liberal Party leader Crin Antonescu - whose party invited the former monarch to speak - was quoted as saying by the Associated Press news agency.
"It is a symbolic gesture that has no connection to the idea of changing Romania's status as a republic," Mr Antonescu added.Test pilot
King Michael I reigned from 1927 to 1930, and again from 1940 to 1947.
In December 1947, Romania's new Communist leaders threatened to carry out mass executions if he refused to abdicate.
In an interview with the BBC's Nick Thorpe, the former monarch described how the authorities had blackmailed him: "If you don't sign this thing now, we're going to have to shoot or kill 1,000 people that are already in prison."
"What do you do in a case like that?"
The king was then banned from returning to Romania for nearly half a century.
The Romanian royal family settled near Geneva in Switzerland, and the former king had to find work.
He said one of his favourite jobs was as a test pilot on private aeroplanes in Europe and the United States.
He met his future wife, Anne of Bourbon-Palma, at the wedding of the future Queen Elizabeth II and the Duke of Edinburgh in London in 1947.
King Michael's Romanian citizenship was restored in 1997.