Can I stop my ex from introducing our child to their new partner?

Unless the new partner poses a danger to your child, you cannot stop the introduction.  There must be specific and serious concerns relating to your child’s safety and welfare. It is not enough to oppose or prevent the introduction without sufficient evidence. The introduction of a new partner is generally not considered a “key decision” that requires the agreement of both parents. You can try to discuss with your ex how and when the introduction should happen, or agree a certain period of time before the introduction is made.

If you have serious concerns about your child’s safety or wellbeing around the new partner (or any person), you should consider taking legal action to protect your child, such as a Prohibited Steps Order.