Kate Torpey was expecting her third baby in three years, but when she told bosses of the , company that owns the upmarket clothing chains Jigsaw and Kew, she was told 'it really isn't ideal'.
Now Ms Torpey, who earned £150,000 a year for her role at Robinson Webster Holdings, is suing for sex discrimination, unfair dismissal and discrimination on the grounds of maternity.
Her allegations involve John Robinson, the owner of Jigsaw who appointed the Duchess of Cambridge as an accessories buyer in 2006.
Mr Robinson and his wife Belle are reported to be family friends of the Duchess's parents, Michael and Carole Middleton.
Both Robinson Webster Holdings and Mr Robinson deny the claims.
Ms Torpey told the tribunal that she had been 'worried' about taking maternity leave, because Mr Robinson had 'proudly' told her how his wife had returned to work within days of giving birth.
"I felt he was suggesting that he thought other women took an unnecessarily long time off after giving birth," she said.
"John said that he thought it very difficult to do my job with a young child. He explained to me how he wasn't that involved with his children but that Belle [his wife] certainly couldn't do it.
"I also remember that he said if I wanted two children then trying to do my job would be 'totally useless'."
Ms Torpey claimed Mr Robinson 'vetoed' her for a promotion at a board meeting in Jan 2010 - the same day she told him she was pregnant again.
Referring to an email sent in November 2010, while she was still on maternity leave, she highlighted a section in which Mr Robinson said she had 'lost her confidence' and that her 'main aim was to have children'.
Ms Torpey said she was then offered a part-time group strategic planning director's role before returning to work on a £125,000 salary.
She went back to work in May 2011 and was reappointed as a director, before announcing her third pregnancy.
She alleges Charlie Atterton, another director, then told her: "It really isn't ideal."
She was signed off sick with anxiety in Nov 2011 and resigned the next month.
Mr Robinson says the decisions were not made due to Ms Torpey's pregnancy, but because the role required somebody working five days per week.
"I did say that doing her job with children would be 'difficult' - because that's my opinion, but I certainly didn't say that trying to do her job with two children would be 'totally useless'," he said.
The tribunal continues.