Meghan Markle filed a formal complaint with British broadcaster ITV, after a presenter criticised her claims against the royal family and later quit.
Piers Morgan left his role as host of Good Morning Britain on Tuesday following a scathing attack on the Duchess of Sussex's interview with US chat show host Oprah Winfrey.
She and her husband, Prince Harry, accused the royal family of racism, while the former television actress said she had suicidal thoughts during her time in Britain.
Former CNN host Morgan's comments that he did not believe her sparked 41 000 complaints to Britain's broadcasting regulator Ofcom.
Britain's domestic Press Association news agency said it understood Meghan formally complained to ITV before he resigned, confirming a report in the Daily Telegraph newspaper.
The complaint focused on how his remarks may affect those trying to deal with their own mental health problems, it added.
It did not concern his repeated criticism of her or allegations of racism, which have rocked the monarchy.
Morgan, a former tabloid newspaper editor, has been a consistent critic of Markle after she cut off contact with him after she met Harry and they married in 2018.
On Tuesday, Morgan stormed off the set of Good Morning Britain as he clashed with a fellow presenter who defended the duchess.
In a tweet as the programme aired on Wednesday, Morgan said he stood by his remarks and said he would fight for freedom of speech.
"On Monday, I said I didn't believe Meghan Markle in her Oprah interview. I've had time to reflect on this opinion, and I still don't," he wrote.
Buckingham Palace on Tuesday responded to the explosive claims.
Queen Elizabeth II said Meghan and Harry, who quit royal life last year, and their son Archie would remain "much-loved family members".
But she also said the accusations would be dealt with "privately".
Asked to respond to Buckingham Palace's statement, a spokesman for Meghan and Harry said they would not be commenting any further.