In Season 13 of "Grey's Anatomy," Meredith is going to lose one another person who stood by her through thick and thin. Maggie is going to learn the truth about Meredith's fling with Nathan in the upcoming season and this will create a strain in their relationship, as Maggie wouldn't be too pleased with Meredith keeping her in the dark.

The penultimate episode of Season 12 saw Meredith hooking up with Nathan, only to be told by her sister the next day that she fancied the New Zealand doctor. Meredith decided to keep mum about her fling, but nothing stays a secret for long in Grey Sloan Memorial Hospital. According to reports, Maggie will learn the truth about Meredith and Nathan's fling in Season 13 episode 2.

"One of the things that we know about Maggie is that she is really a stickler for honesty and the truth," actress Kelly McCreary, who plays Maggie, told TV Guide, previewing Maggie and Meredith's relationship.

"In her first season, she really holds it against Richard (James Pickens Jr.) that he didn't tell her [he was her father] right away, that he withheld the truth for any length of time. To me, that's an indication of how we can expect Maggie to feel about any lack of honesty, any lack of full transparency and disclosure in a relationship — especially with somebody that she trusts and, more than trusts, really relies upon as much as Meredith."

McCreary also revealed that Season 13 will be more about the original cast members, which include Meredith, Alex, Bailey and Richard.

Those characters are so rich and they have so much meaning for our audience. I think it'll be wonderful to spend some more time with them," said McCreary.

"Grey's Anatomy" returns Thursday, Sept. 22 at 8 pm ET on ABC.