The pair starred opposite each other in 2001 romantic comedy Bridget Jones’s Diary and in its 2004 follow up The Edge of Reason.
Appearing on SiriusXM’s The Jess Cagle Show, Grant opened up about his continued friendship with the US actor.
“I love Renée, she's one of the few actresses I haven't fallen out with,” Grant admitted.
“We got on very well together and we still exchange long emails. Hers in particular, at least 70 pages each, interesting stuff, but quite hard to decipher. She's a properly good egg and a genius."
Grant then went on to praise Zellweger for her Oscar-winning turn in 2019 biopic Judy, asking: “Did you see her Judy Garland? About as good as acting gets.”
Grant has previously admitted to being “hated” by a number of his female co-stars, including Julianne Moore, Rachel Weisz and Drew Barrymore.
The actor said that he made Barrymore cry while starring opposite her in Music and Lyrics, explaining: “She made the mistake of giving me notes.”
While Grant didn’t return to the Bridget Jones franchise alongside Zellweger and Colin Firth for 2016’s Bridget Jones’s Baby, the actor has said that he could potentially revive the character of Daniel Cleaver for the right story.
Earlier this week, it was revealed that Grant is teaming up with Black Mirror creator Charlie Brooker for a mockumentary about 2020.
The 60-year-old actor will star as a historian in the mockumentary, which is going to air on Netflix.