"[It's] all blood under the bridge," Thompson said. "You can't hold on to anything like that. I just think ... pfft. It's pointless. I haven't got the energy for it. Helena and I made our peace years and years ago."
"Much Ado About Nothing" and "Dead Again" co-stars Thompson and Branagh split after six years of marriage in 1995. Branagh began an affair with Bonham Carter on the set of "Mary Shelley's Frankenstein" in 1994 and their courtship lasted until 1999, TVGuide.com said.
Thompson has been married to her "Sense and Sensibility" co-star Greg Wise for 10 years while Bonham Carter has been dating her frequent director Tim Burton since 2001. Both couples have two children.
Branagh married art director Lindsay Brunnock in 2003.
Thompson joked to The Times she understands what Branagh saw in Bonham Carter.
"Oh, we are [alike]," she said. "Being slightly mad and a bit fashion-challenged. Perhaps that's why Ken loved us both. She's a wonderful woman, Helena."
Coincidentally, Thompson, Bonham Carter and Branagh have all since appeared in Harry Potter films.