While the pair battled to keep tabs on unruly aliens living among humans, their relationship blossomed. Now there will be a new partner to work with.
"There will be a prominent woman in black in the fourth [film]," MacDonald told Newsbeat.
Parkes also commented that fans should "never count Will out," after rumours surfaced that Smith might not make an appearance this time around.
"We are quite early on in it," he said. "We sort of looked at the first three in retrospect as a bit of a trilogy."
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He added that it was exciting to work on the project once more, with the last film Men in Black 3 made in 2012.
"Now we are looking at a reinvention," Parkes added. "But it's a wonderful world to get back into."
- nzherald.co.nz