The couple were runners up on the dating show in 2016.
They've since married and a series of TV, clothing and magazine deals have led them to amass a reported £4.2 million fortune.
The pair's total, as estimated by heat magazine’s Under 30 Rich List 2019, makes them the richest stars to have appeared on the ITV2 reality series.
The news comes as Alex and Olivia's new TV show airs on TLC.
Olivia and Alex: Happily Ever After follows the now married couple in their day to day lives.
A trailer for the series released earlier this year saw the pair discussing starting a family together.
Alex says: "I'm 28 this year, I want to be one of them young dads."
But Olivia responds: "You don't realise how much a baby will change your life!"
She is later seen telling her mum: "Alex wants a child now, he always talks to me about it."
Hinting that she's not ready to become a mother yet, Olivia added: 'I'm not ready to let go of my youth!'
Olivia & Alex's series airs on TLC at 9PM on Friday nights. TLC is available on Sky channel 831, Virgin and BT 377.
Meanwhile, other reality stars cashing in according to the rich list rankings are the likes of former TOWIE stars Billie Faiers (£3.6 million), her sister Sam Faiers (£6.3 million) and Joey Essex (£6.3 million).
Former X Factor winners Little Mix are said to be sitting on a combined fortune of £50 million between them but it's Ed Sheeran who tops the list with an estimated net worth of £170 million.
He replaces Adele in the top spot after the singer turned 31 earlier this year.
heat's 30 Richest Celebrities 30 and Under appears in this week’s heat magazine, on sale now.