It took four years, but state Senate Republicans have finally repaid a $50,000 loan from their crooked old boss, Dean Skelos.

Campaign records show the loan was quietly settled on July 16.

The former majority leader, once one of the most powerful officials in the state, had advanced $100,000 to the Senate Republicans in 2014 to help maintain their majority.

The first half of the IOU was quickly repaid. But after Skelos was indicted for corruption in 2015, the final repayment was put on hold — until three months ago.

Skelos can use the cash. After drawing down $2.4 million for criminal defense lawyers, his campaign account is down to $43,868.

Democrats were quick to pounce on the loan repayment.

“I’m sure the Republican donors will appreciate to know that their money is going to a corrupt convicted felon rather than to candidates,” said Senate Democratic spokesman Mike Murphy.

In July, a federal jury found Skelos and his son, Adam, guilty of bribery and extortion, for strong-arming companies into giving Adam do-nothing jobs and consulting gigs.

Senate Democrats are not without stain, however.

Two of their former leaders, Malcolm Smith and John Sampson, were sentenced to prison for crimes in office.

And former Democratic Assembly Speaker Sheldon Silver was convicted in May — for a second time — of selling his office for $4 million in kickbacks.

The Senate GOP still has more than $2.3 million in its kitty following an $800,000 transfer from the current majority leader, John Flanagan.

The GOP holds a 32-31 majority in the Senate which is on the line in the Nov. 6 election.