Charles Haughey has rejected the notion that he would divert money from a fund set up to save Brian Lenihan's life.
Mr Haughey's evidence to the Moriarty Tribunal is currently being read into the public record.
Justice Moriarty was told that two cheques totalling £30,000, endorsed by Charles Haughey, ended up in an account for Celtic Helicopters at Dublin Airport.
The first, for £10,000 was made out personally to Charles Haughey from the Irish Permanent Building Society.
The second from the Irish Permanent was made out to the Brian Lenihan Fund.
Mr Haughey said he could not explain how the £30,000 ended up in the Celtic Helicopters account.
Mr Haughey described himself as being closer to Brian Lenihan than one of his own brothers.