The wife and brother-in-law of the Earl of Shaftesbury, Anthony Ashley-Cooper, have been arrested by French police on suspicion of his murder.
The Earl has not contacted family or friends since 5 November
Djamilia M'Barek, 37, was arrested in the resort town of Cannes on Friday, while Mohammed M'Barek, 40, was arrested on Saturday in Munich.
The 66-year-old earl disappeared from Cannes in November last year, only days before he was due to return to the UK.
Police said in December that they were treating his disappearance as a murder.
Mohammed M'Barek will be transferred to France to face questioning.
The earl was estranged from Djamilia M'Barek, his third wife, at the time of his disappearance.
They were married in 2002, reports said.
The BBC's Allan Little in Paris said it was believed the earl also had a girlfriend in the nearby resort town of Antibes at the time.
"It was well-known that he was a frequenter of nightclubs, that he had a very eccentric lifestyle. He would often fly between his homes in the south of England and the south of France without informing any member of his family where he was going," he said.
"When he disappeared at first a lot of people who knew him thought that he had just disappeared for a few days."
Senior detectives from Sussex police flew to Nice a few days later to assist French police.
The earl has not been seen since leaving this Cannes hotel
The detectives, from the force's major crime branch, spent four days discussing the investigation with their French counterparts.
Lady Christina Shaftesbury, the earl's ex-wife, who lives at the family estate in Wimborne St Giles, Dorset, travelled to France with the officers.
The earl had been due to return to Britain on 10 November. He was last seen checking out of his hotel in Cannes.
His body has not been found.
In late December, the earl's son Lord Ashley issued a statement saying that the family "feared the worst".