An 80-year-old man launched a hammer attack on his wife's 63-year-old lover after catching the couple kissing, a court heard.
Stuart Pask, a retired production engineer, battered John Hanson over the head repeatedly in front of horrified commuters at Waterloo Station.
Mr Hanson crouched under a 'rain of blows' as Pask's wife Teresa, 61, looked on.
After being restrained by two off-duty policemen Pask said: 'He's been f***ing my wife.'
Turning to Mrs Hanson, a software project manager, the husband said: 'You kissed him four times.
'He asked for it and he got it. I've spent the last year doing up our house. They've probably been in my bed and in the whirlpool which I fitted.'
However, Mrs Pask was horrified when her husband was jailed. She said: 'This isn't justice - this is a total waste of everybody's money.'
Blackfriars Crown Court heard Mrs Pask and Mr Hanson had an affair but they claimed they ended it off when her husband found out.
The married couple stayed together, living at their home in Surrey, and had recently enjoyed a holiday in America when their lives unravelled for a second time.
Philip Jones, prosecuting, said the former lovers met through a mutual interest in genealogy.
He said:'Mr Pask is a gentleman aged 80 and his wife Teresa who is some 19 years his junior, have been married for 33 years
'Mr Pask is a man of previous good character. Quite a few years ago he and his wife both developed an interest in genealogy.
'It was through that mutual interest that they came to know the complainant in this case, Mr Hanson.
'It came about towards the beginning of last year that Mrs Pask and Mr Hanson began an affair and it lasted for some months.
'It concluded in October 2009 after it was discovered by Mr Pask. Mr Pask was very angry about it but he was assured it was to end.'
The Pasks stayed together, living at their home in Surrey, and had recently had a 'very successful' holiday in America.
However, their lives unravelled for a second time, as Mr Jones continued: 'On 7th August this year they encountered Mr Hanson at a reception and it somehow started up in the defendant's mind his feelings about this affair and that Mr Hanson had got away with having an affair with his wife.
'Then on 10th August Mrs Pask, having maintained her interest in genealogy, was to attend a committee meeting at the premises of the Society of Genealogists in Clerkenwell.
'She assured her husband that she would not spend any time alone with Mr Hanson.
'Mr Pask knew the time she would be getting her train home from Waterloo Station.
'He had reservations but she assured him she would not see him alone.
'It was a meeting that went on until the early evening, but after the meeting had finished she did spend some time with Mr Hanson.'
The court head Mrs Pask shared a bottle of wine with Mr Hanson at the Royal Festival Hall before walking back to Waterloo, where they kissed goodbye on the concourse.
'The time arrived at which Mrs Pask had to catch her train back, having spent a pleasant time together.
Mr Jones continued: 'Mr Hanson made his way towards Marks and Spencer for some water and suddenly he saw coming towards him somebody he recognised to be the defendant.
'He saw the defendant had something in his right hand. It was in fact a hammer, concealed with a white plastic carrier bag.
'The defendant ran up to Mr Hanson and took hold of his shoulder. With the hammer in his right hand he struck Mr Hanson a number of times on the head and two blows landed on his arm and shoulder.
'Mr Hanson crouched and raised his arms and tried to protect himself. The blows rained upon him.
'He did not recall being kicked though other witnesses spoke of this happening.'
Pask, of Byfleet Road, New Haw, Addlestone, Surrey, admitted assault occasioning actual bodily harm.
His wife was stunned and in tears as he was led away. She said as the judge left the room: 'I'm sorry, I'm a bit confused. Has he just sentenced my husband to two years imprisonment?
'He's just sent an 80-year-old to prison for two years?.' Outside court she said: 'You see in the papers people getting away with much more serious things. I'm overwhelmed with disbelief.
'He didn't think of the consequences - he had that flash of anger.'
Mrs Pask said she was worried about her husband's safety in prison, and did not even know where he was being taken.
She added: 'He's never even been in a court in his life. The people that should have been in court today is John and me, not Stuart.
'This isn't justice - this is a total waste of everybody's money.'
Tim Brown, defending, said she felt partly responsible for the attack even though her husband 'makes it clear he takes responsibility for his behaviour'.
Mr Brown pleaded for any jail sentence to be suspended, his lawyer added: 'He and his wife are together.
'There is no contact with Mr Hanson. There are no social matters. Had they taken this view six months ago they know Mr Pask wouldn't have been here today.
'They take the view that if they are to make anything of their marriage this has to be the case. They are having counselling. It is clear there's a lot of work to be done.
'There is a lot of resentment from Mr Pask and a lot of guilt on the part of Mrs Pask.' Jailing Pask, Judge David Martineau said he had taken into account that a 'red mist' descended.
He accepted his behaviour was completely out of character - provoked by a feeling of having been 'greatly wronged'.
But he added: 'This was a thoroughly pre-meditated attack with a hammer, aimed at the head, motivated by revenge which could very easily have resulted in serious harm.
'It is very surprising that it didn't so result. It was committed in full view of a great many people at Waterloo Station.
'If you had any previous convictions and if you were 10 or more years younger it seems to me it would inevitably have been a substantial custodial sentence.'