In an appearance on Bravo's "Watch What Happens Live," Hannigan, who currently stars in CBS' "How I Met Your Mother," spilled some beans on her former colleague to host Andy Cohen.
When asked during the show's "Plead the Fifth" segment who was most "annoyed" by the end of the show's seven-season run, Hannigan piped up, "Sarah. She had a big career going."
She added with a bit of a snark, "It was a lot of work."
Gellar's star has fallen in the last several years. Her movie career never took off, and her last TV series, "Ringer," was yanked last year after one season.
[For the Record, 2:44 p.m. PDT May 9: An earlier version of this online post, including the headline and photo caption, misspelled the last name of Sarah Michelle Gellar as Geller.]