So why is Disgraced Former Minister Peter Mandelson a disgraced former minister? Well amazingly enough, he has been disgraced and forced to resign as a minister more than once.
He will now be referred to as twice Disgraced Former Minister Peter Mandelson.
There we go.

Disgrace Peter Mandelson bought a house.
Not the sort of house you or I could buy but one so expensive that he was £370k short of the money needed
Mandelson asked a friend, Geoffrey Robinson, to borrow the money
to aid their friendship & so aid the political progress of Robinson

During the Commons Standards and Privileges Committee hearings, the Disgraced Serving Minister Because He Hadn't At This Point Had The Good Grace To Resign Peter Mandelson denied the loan was politically motivated and instead said it was one friend helping another.

So what caused Disgraced Former Minister Peter Mandelson to become disgraced (first time round)? Well simply put, he did not declare this loan. This is an important thing for a politician. Someone gives a politician £370k and the public are due to know about it. It is important

Say one MP loans one of the closest allies of the future PM £370k, and then the MP gets appointed to the cabinet. We should know.
So there we have it. How Minister Peter Mandelson became Disgraced Former Minister Peter Mandelson

Of course, we are not done there. There is far more to come. Allegations of lying to committees along with whole new fresh scandals! how Disgraced Former Minister Peter Mandelson become Twice Disgraced Former Minister Peter Mandelson?
We shall see a little later

Peter Mandelson resigned from the Cabinet for a second time in 2001,having gotten caught up in a row over a passport application from Indian billionaire Srichand Hinduja.
that is far from the end of the numerous scandals Twice disgraced former minister Mandelson was embroiled in