Having worked with Mostert for six of the last seven Supercars seasons, it was widely expected that De Borre would follow the star driver to WAU.
That’s now been confirmed, co-team principal Mathew Nilsson certain the move will help Mostert acclimatize to new surroundings.
“It’s wonderful to have Adam join the engineering group here at Walkinshaw Andretti United,” said Nilsson.
"He has a fantastic pedigree in motorsport, and will certainly add to the experience of the group as we look to continue our progression.
“Having that stable relationship with Chaz is also critical. There will be a lot of new elements for Chaz to adjust to early on in the season, so to have that familiarity between the two of them is a huge bonus, and a formula that is proven.”
De Borre added: “It’s really exciting to be joining such a strong and experienced group at Walkinshaw Andretti United in 2020.
"It’s a team with so much history and I can’t wait to add to with Chaz.
“To be able to stay with Chaz for the start of our seventh season together is fantastic and I hope all the experience gained over the past six seasons will help us guide the car to the front.”