The two have known one another since their days as students at Queen s University Belfast.
Mrs Foster was recruited into the Queen s Unionist Association by Mr Weir and served as chairwoman from 1992 to 1993.
The pair later joined the Ulster Unionist Party around the same time and were both opposed to the 1998 Good Friday Agreement.
They were also part of a group within the UUP known as the baby barristers who were heavily critical of then-leader David Trimble.
Both would leave the UUP and join the DUP - Mr Weir in 2002 and Mrs Foster two years later.
When Mrs Foster became first minister in 2016, she rewarded Mr Weir by appointing him as education minister.