Louth-born animal health entrepreneur Eddie Haughey, who was also known by his former title Lord Ballyedmond, died in a helicopter crash in 2014.
His Norbrook Laboratories business is now owned by his wife Mary and the family, to whom 104m of assets, including properties and farmland, were transferred at the end of 2015.
The family also owns castles in Northern Ireland and Cumbria in the north of England, as well as an estate in Norfolk. A house in one of London's most expensive postcodes, Belgrave Square, which was bought in 2006 for 18m, is probably worth three times that now. A planning application seeking to make relatively minor improvements that was made last year by Lady Ballyedmond shows a house described as a family home and rich in architectural detail, complete with a huge dining room.