The Black Cats this week sealed a £1.4 million deal with St Truiden for Mignolet, who became the second of Steve Bruce's three signings so far this summer.
But the 21-year-old was destined to snub a switch to Wearside in favour of joining Dutch giants PSV Eindhoven - until his dad, Stefan, stepped in.
"But when he said at one point that he would choose PSV because it would make us happy, I intervened.
"This was about his career, and he had to take the right step to move it forward.
"We told him he would always have our 100 per cent support wherever he goes."
And so dad told his lad to board a plane to England.
"It's a different world (in the Premier League," added Stefan. "I had to read the numbers on Simon's deal twice. The money was a shock.
"Simon will earn three to four times what he does now."